LLVM 19.0.0git
JumpThreading.cpp
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1//===- JumpThreading.cpp - Thread control through conditional blocks ------===//
2//
3// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
4// See https://llvm.org/LICENSE.txt for license information.
5// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
6//
7//===----------------------------------------------------------------------===//
8//
9// This file implements the Jump Threading pass.
10//
11//===----------------------------------------------------------------------===//
12
14#include "llvm/ADT/DenseMap.h"
15#include "llvm/ADT/DenseSet.h"
16#include "llvm/ADT/MapVector.h"
17#include "llvm/ADT/STLExtras.h"
20#include "llvm/ADT/Statistic.h"
24#include "llvm/Analysis/CFG.h"
30#include "llvm/Analysis/Loads.h"
37#include "llvm/IR/BasicBlock.h"
38#include "llvm/IR/CFG.h"
39#include "llvm/IR/Constant.h"
41#include "llvm/IR/Constants.h"
42#include "llvm/IR/DataLayout.h"
43#include "llvm/IR/DebugInfo.h"
44#include "llvm/IR/Dominators.h"
45#include "llvm/IR/Function.h"
46#include "llvm/IR/InstrTypes.h"
47#include "llvm/IR/Instruction.h"
50#include "llvm/IR/Intrinsics.h"
51#include "llvm/IR/LLVMContext.h"
52#include "llvm/IR/MDBuilder.h"
53#include "llvm/IR/Metadata.h"
54#include "llvm/IR/Module.h"
55#include "llvm/IR/PassManager.h"
58#include "llvm/IR/Type.h"
59#include "llvm/IR/Use.h"
60#include "llvm/IR/Value.h"
65#include "llvm/Support/Debug.h"
72#include <algorithm>
73#include <cassert>
74#include <cstdint>
75#include <iterator>
76#include <memory>
77#include <utility>
78
79using namespace llvm;
80using namespace jumpthreading;
81
82#define DEBUG_TYPE "jump-threading"
83
84STATISTIC(NumThreads, "Number of jumps threaded");
85STATISTIC(NumFolds, "Number of terminators folded");
86STATISTIC(NumDupes, "Number of branch blocks duplicated to eliminate phi");
87
89BBDuplicateThreshold("jump-threading-threshold",
90 cl::desc("Max block size to duplicate for jump threading"),
92
95 "jump-threading-implication-search-threshold",
96 cl::desc("The number of predecessors to search for a stronger "
97 "condition to use to thread over a weaker condition"),
99
101 "jump-threading-phi-threshold",
102 cl::desc("Max PHIs in BB to duplicate for jump threading"), cl::init(76),
103 cl::Hidden);
104
106 "jump-threading-across-loop-headers",
107 cl::desc("Allow JumpThreading to thread across loop headers, for testing"),
108 cl::init(false), cl::Hidden);
109
111 DefaultBBDupThreshold = (T == -1) ? BBDuplicateThreshold : unsigned(T);
112}
113
114// Update branch probability information according to conditional
115// branch probability. This is usually made possible for cloned branches
116// in inline instances by the context specific profile in the caller.
117// For instance,
118//
119// [Block PredBB]
120// [Branch PredBr]
121// if (t) {
122// Block A;
123// } else {
124// Block B;
125// }
126//
127// [Block BB]
128// cond = PN([true, %A], [..., %B]); // PHI node
129// [Branch CondBr]
130// if (cond) {
131// ... // P(cond == true) = 1%
132// }
133//
134// Here we know that when block A is taken, cond must be true, which means
135// P(cond == true | A) = 1
136//
137// Given that P(cond == true) = P(cond == true | A) * P(A) +
138// P(cond == true | B) * P(B)
139// we get:
140// P(cond == true ) = P(A) + P(cond == true | B) * P(B)
141//
142// which gives us:
143// P(A) is less than P(cond == true), i.e.
144// P(t == true) <= P(cond == true)
145//
146// In other words, if we know P(cond == true) is unlikely, we know
147// that P(t == true) is also unlikely.
148//
150 BranchInst *CondBr = dyn_cast<BranchInst>(BB->getTerminator());
151 if (!CondBr)
152 return;
153
154 uint64_t TrueWeight, FalseWeight;
155 if (!extractBranchWeights(*CondBr, TrueWeight, FalseWeight))
156 return;
157
158 if (TrueWeight + FalseWeight == 0)
159 // Zero branch_weights do not give a hint for getting branch probabilities.
160 // Technically it would result in division by zero denominator, which is
161 // TrueWeight + FalseWeight.
162 return;
163
164 // Returns the outgoing edge of the dominating predecessor block
165 // that leads to the PhiNode's incoming block:
166 auto GetPredOutEdge =
167 [](BasicBlock *IncomingBB,
168 BasicBlock *PhiBB) -> std::pair<BasicBlock *, BasicBlock *> {
169 auto *PredBB = IncomingBB;
170 auto *SuccBB = PhiBB;
172 while (true) {
173 BranchInst *PredBr = dyn_cast<BranchInst>(PredBB->getTerminator());
174 if (PredBr && PredBr->isConditional())
175 return {PredBB, SuccBB};
176 Visited.insert(PredBB);
177 auto *SinglePredBB = PredBB->getSinglePredecessor();
178 if (!SinglePredBB)
179 return {nullptr, nullptr};
180
181 // Stop searching when SinglePredBB has been visited. It means we see
182 // an unreachable loop.
183 if (Visited.count(SinglePredBB))
184 return {nullptr, nullptr};
185
186 SuccBB = PredBB;
187 PredBB = SinglePredBB;
188 }
189 };
190
191 for (unsigned i = 0, e = PN->getNumIncomingValues(); i != e; ++i) {
192 Value *PhiOpnd = PN->getIncomingValue(i);
193 ConstantInt *CI = dyn_cast<ConstantInt>(PhiOpnd);
194
195 if (!CI || !CI->getType()->isIntegerTy(1))
196 continue;
197
200 TrueWeight, TrueWeight + FalseWeight)
202 FalseWeight, TrueWeight + FalseWeight));
203
204 auto PredOutEdge = GetPredOutEdge(PN->getIncomingBlock(i), BB);
205 if (!PredOutEdge.first)
206 return;
207
208 BasicBlock *PredBB = PredOutEdge.first;
209 BranchInst *PredBr = dyn_cast<BranchInst>(PredBB->getTerminator());
210 if (!PredBr)
211 return;
212
213 uint64_t PredTrueWeight, PredFalseWeight;
214 // FIXME: We currently only set the profile data when it is missing.
215 // With PGO, this can be used to refine even existing profile data with
216 // context information. This needs to be done after more performance
217 // testing.
218 if (extractBranchWeights(*PredBr, PredTrueWeight, PredFalseWeight))
219 continue;
220
221 // We can not infer anything useful when BP >= 50%, because BP is the
222 // upper bound probability value.
223 if (BP >= BranchProbability(50, 100))
224 continue;
225
226 uint32_t Weights[2];
227 if (PredBr->getSuccessor(0) == PredOutEdge.second) {
228 Weights[0] = BP.getNumerator();
229 Weights[1] = BP.getCompl().getNumerator();
230 } else {
231 Weights[0] = BP.getCompl().getNumerator();
232 Weights[1] = BP.getNumerator();
233 }
234 setBranchWeights(*PredBr, Weights);
235 }
236}
237
240 auto &TTI = AM.getResult<TargetIRAnalysis>(F);
241 // Jump Threading has no sense for the targets with divergent CF
243 return PreservedAnalyses::all();
244 auto &TLI = AM.getResult<TargetLibraryAnalysis>(F);
245 auto &LVI = AM.getResult<LazyValueAnalysis>(F);
246 auto &AA = AM.getResult<AAManager>(F);
247 auto &DT = AM.getResult<DominatorTreeAnalysis>(F);
248
249 bool Changed =
250 runImpl(F, &AM, &TLI, &TTI, &LVI, &AA,
251 std::make_unique<DomTreeUpdater>(
253 std::nullopt, std::nullopt);
254
255 if (!Changed)
256 return PreservedAnalyses::all();
257
258
260
261#if defined(EXPENSIVE_CHECKS)
262 assert(getDomTreeUpdater()->getDomTree().verify(
263 DominatorTree::VerificationLevel::Full) &&
264 "DT broken after JumpThreading");
265 assert((!getDomTreeUpdater()->hasPostDomTree() ||
266 getDomTreeUpdater()->getPostDomTree().verify(
268 "PDT broken after JumpThreading");
269#else
270 assert(getDomTreeUpdater()->getDomTree().verify(
271 DominatorTree::VerificationLevel::Fast) &&
272 "DT broken after JumpThreading");
273 assert((!getDomTreeUpdater()->hasPostDomTree() ||
274 getDomTreeUpdater()->getPostDomTree().verify(
276 "PDT broken after JumpThreading");
277#endif
278
279 return getPreservedAnalysis();
280}
281
283 TargetLibraryInfo *TLI_,
285 AliasAnalysis *AA_,
286 std::unique_ptr<DomTreeUpdater> DTU_,
287 std::optional<BlockFrequencyInfo *> BFI_,
288 std::optional<BranchProbabilityInfo *> BPI_) {
289 LLVM_DEBUG(dbgs() << "Jump threading on function '" << F_.getName() << "'\n");
290 F = &F_;
291 FAM = FAM_;
292 TLI = TLI_;
293 TTI = TTI_;
294 LVI = LVI_;
295 AA = AA_;
296 DTU = std::move(DTU_);
297 BFI = BFI_;
298 BPI = BPI_;
299 auto *GuardDecl = F->getParent()->getFunction(
300 Intrinsic::getName(Intrinsic::experimental_guard));
301 HasGuards = GuardDecl && !GuardDecl->use_empty();
302
303 // Reduce the number of instructions duplicated when optimizing strictly for
304 // size.
305 if (BBDuplicateThreshold.getNumOccurrences())
306 BBDupThreshold = BBDuplicateThreshold;
307 else if (F->hasFnAttribute(Attribute::MinSize))
308 BBDupThreshold = 3;
309 else
310 BBDupThreshold = DefaultBBDupThreshold;
311
312 // JumpThreading must not processes blocks unreachable from entry. It's a
313 // waste of compute time and can potentially lead to hangs.
315 assert(DTU && "DTU isn't passed into JumpThreading before using it.");
316 assert(DTU->hasDomTree() && "JumpThreading relies on DomTree to proceed.");
317 DominatorTree &DT = DTU->getDomTree();
318 for (auto &BB : *F)
319 if (!DT.isReachableFromEntry(&BB))
320 Unreachable.insert(&BB);
321
324
325 bool EverChanged = false;
326 bool Changed;
327 do {
328 Changed = false;
329 for (auto &BB : *F) {
330 if (Unreachable.count(&BB))
331 continue;
332 while (processBlock(&BB)) // Thread all of the branches we can over BB.
333 Changed = ChangedSinceLastAnalysisUpdate = true;
334
335 // Jump threading may have introduced redundant debug values into BB
336 // which should be removed.
337 if (Changed)
339
340 // Stop processing BB if it's the entry or is now deleted. The following
341 // routines attempt to eliminate BB and locating a suitable replacement
342 // for the entry is non-trivial.
343 if (&BB == &F->getEntryBlock() || DTU->isBBPendingDeletion(&BB))
344 continue;
345
346 if (pred_empty(&BB)) {
347 // When processBlock makes BB unreachable it doesn't bother to fix up
348 // the instructions in it. We must remove BB to prevent invalid IR.
349 LLVM_DEBUG(dbgs() << " JT: Deleting dead block '" << BB.getName()
350 << "' with terminator: " << *BB.getTerminator()
351 << '\n');
352 LoopHeaders.erase(&BB);
353 LVI->eraseBlock(&BB);
354 DeleteDeadBlock(&BB, DTU.get());
355 Changed = ChangedSinceLastAnalysisUpdate = true;
356 continue;
357 }
358
359 // processBlock doesn't thread BBs with unconditional TIs. However, if BB
360 // is "almost empty", we attempt to merge BB with its sole successor.
361 auto *BI = dyn_cast<BranchInst>(BB.getTerminator());
362 if (BI && BI->isUnconditional()) {
363 BasicBlock *Succ = BI->getSuccessor(0);
364 if (
365 // The terminator must be the only non-phi instruction in BB.
366 BB.getFirstNonPHIOrDbg(true)->isTerminator() &&
367 // Don't alter Loop headers and latches to ensure another pass can
368 // detect and transform nested loops later.
369 !LoopHeaders.count(&BB) && !LoopHeaders.count(Succ) &&
372 // BB is valid for cleanup here because we passed in DTU. F remains
373 // BB's parent until a DTU->getDomTree() event.
374 LVI->eraseBlock(&BB);
375 Changed = ChangedSinceLastAnalysisUpdate = true;
376 }
377 }
378 }
379 EverChanged |= Changed;
380 } while (Changed);
381
382 LoopHeaders.clear();
383 return EverChanged;
384}
385
386// Replace uses of Cond with ToVal when safe to do so. If all uses are
387// replaced, we can remove Cond. We cannot blindly replace all uses of Cond
388// because we may incorrectly replace uses when guards/assumes are uses of
389// of `Cond` and we used the guards/assume to reason about the `Cond` value
390// at the end of block. RAUW unconditionally replaces all uses
391// including the guards/assumes themselves and the uses before the
392// guard/assume.
394 BasicBlock *KnownAtEndOfBB) {
395 bool Changed = false;
396 assert(Cond->getType() == ToVal->getType());
397 // We can unconditionally replace all uses in non-local blocks (i.e. uses
398 // strictly dominated by BB), since LVI information is true from the
399 // terminator of BB.
400 if (Cond->getParent() == KnownAtEndOfBB)
401 Changed |= replaceNonLocalUsesWith(Cond, ToVal);
402 for (Instruction &I : reverse(*KnownAtEndOfBB)) {
403 // Replace any debug-info record users of Cond with ToVal.
404 for (DPValue &DPV : filterDbgVars(I.getDbgRecordRange()))
405 DPV.replaceVariableLocationOp(Cond, ToVal, true);
406
407 // Reached the Cond whose uses we are trying to replace, so there are no
408 // more uses.
409 if (&I == Cond)
410 break;
411 // We only replace uses in instructions that are guaranteed to reach the end
412 // of BB, where we know Cond is ToVal.
414 break;
415 Changed |= I.replaceUsesOfWith(Cond, ToVal);
416 }
417 if (Cond->use_empty() && !Cond->mayHaveSideEffects()) {
418 Cond->eraseFromParent();
419 Changed = true;
420 }
421 return Changed;
422}
423
424/// Return the cost of duplicating a piece of this block from first non-phi
425/// and before StopAt instruction to thread across it. Stop scanning the block
426/// when exceeding the threshold. If duplication is impossible, returns ~0U.
428 BasicBlock *BB,
429 Instruction *StopAt,
430 unsigned Threshold) {
431 assert(StopAt->getParent() == BB && "Not an instruction from proper BB?");
432
433 // Do not duplicate the BB if it has a lot of PHI nodes.
434 // If a threadable chain is too long then the number of PHI nodes can add up,
435 // leading to a substantial increase in compile time when rewriting the SSA.
436 unsigned PhiCount = 0;
437 Instruction *FirstNonPHI = nullptr;
438 for (Instruction &I : *BB) {
439 if (!isa<PHINode>(&I)) {
440 FirstNonPHI = &I;
441 break;
442 }
443 if (++PhiCount > PhiDuplicateThreshold)
444 return ~0U;
445 }
446
447 /// Ignore PHI nodes, these will be flattened when duplication happens.
448 BasicBlock::const_iterator I(FirstNonPHI);
449
450 // FIXME: THREADING will delete values that are just used to compute the
451 // branch, so they shouldn't count against the duplication cost.
452
453 unsigned Bonus = 0;
454 if (BB->getTerminator() == StopAt) {
455 // Threading through a switch statement is particularly profitable. If this
456 // block ends in a switch, decrease its cost to make it more likely to
457 // happen.
458 if (isa<SwitchInst>(StopAt))
459 Bonus = 6;
460
461 // The same holds for indirect branches, but slightly more so.
462 if (isa<IndirectBrInst>(StopAt))
463 Bonus = 8;
464 }
465
466 // Bump the threshold up so the early exit from the loop doesn't skip the
467 // terminator-based Size adjustment at the end.
468 Threshold += Bonus;
469
470 // Sum up the cost of each instruction until we get to the terminator. Don't
471 // include the terminator because the copy won't include it.
472 unsigned Size = 0;
473 for (; &*I != StopAt; ++I) {
474
475 // Stop scanning the block if we've reached the threshold.
476 if (Size > Threshold)
477 return Size;
478
479 // Bail out if this instruction gives back a token type, it is not possible
480 // to duplicate it if it is used outside this BB.
481 if (I->getType()->isTokenTy() && I->isUsedOutsideOfBlock(BB))
482 return ~0U;
483
484 // Blocks with NoDuplicate are modelled as having infinite cost, so they
485 // are never duplicated.
486 if (const CallInst *CI = dyn_cast<CallInst>(I))
487 if (CI->cannotDuplicate() || CI->isConvergent())
488 return ~0U;
489
492 continue;
493
494 // All other instructions count for at least one unit.
495 ++Size;
496
497 // Calls are more expensive. If they are non-intrinsic calls, we model them
498 // as having cost of 4. If they are a non-vector intrinsic, we model them
499 // as having cost of 2 total, and if they are a vector intrinsic, we model
500 // them as having cost 1.
501 if (const CallInst *CI = dyn_cast<CallInst>(I)) {
502 if (!isa<IntrinsicInst>(CI))
503 Size += 3;
504 else if (!CI->getType()->isVectorTy())
505 Size += 1;
506 }
507 }
508
509 return Size > Bonus ? Size - Bonus : 0;
510}
511
512/// findLoopHeaders - We do not want jump threading to turn proper loop
513/// structures into irreducible loops. Doing this breaks up the loop nesting
514/// hierarchy and pessimizes later transformations. To prevent this from
515/// happening, we first have to find the loop headers. Here we approximate this
516/// by finding targets of backedges in the CFG.
517///
518/// Note that there definitely are cases when we want to allow threading of
519/// edges across a loop header. For example, threading a jump from outside the
520/// loop (the preheader) to an exit block of the loop is definitely profitable.
521/// It is also almost always profitable to thread backedges from within the loop
522/// to exit blocks, and is often profitable to thread backedges to other blocks
523/// within the loop (forming a nested loop). This simple analysis is not rich
524/// enough to track all of these properties and keep it up-to-date as the CFG
525/// mutates, so we don't allow any of these transformations.
528 FindFunctionBackedges(F, Edges);
529
530 for (const auto &Edge : Edges)
531 LoopHeaders.insert(Edge.second);
532}
533
534/// getKnownConstant - Helper method to determine if we can thread over a
535/// terminator with the given value as its condition, and if so what value to
536/// use for that. What kind of value this is depends on whether we want an
537/// integer or a block address, but an undef is always accepted.
538/// Returns null if Val is null or not an appropriate constant.
540 if (!Val)
541 return nullptr;
542
543 // Undef is "known" enough.
544 if (UndefValue *U = dyn_cast<UndefValue>(Val))
545 return U;
546
547 if (Preference == WantBlockAddress)
548 return dyn_cast<BlockAddress>(Val->stripPointerCasts());
549
550 return dyn_cast<ConstantInt>(Val);
551}
552
553/// computeValueKnownInPredecessors - Given a basic block BB and a value V, see
554/// if we can infer that the value is a known ConstantInt/BlockAddress or undef
555/// in any of our predecessors. If so, return the known list of value and pred
556/// BB in the result vector.
557///
558/// This returns true if there were any known values.
560 Value *V, BasicBlock *BB, PredValueInfo &Result,
561 ConstantPreference Preference, DenseSet<Value *> &RecursionSet,
562 Instruction *CxtI) {
563 const DataLayout &DL = BB->getModule()->getDataLayout();
564
565 // This method walks up use-def chains recursively. Because of this, we could
566 // get into an infinite loop going around loops in the use-def chain. To
567 // prevent this, keep track of what (value, block) pairs we've already visited
568 // and terminate the search if we loop back to them
569 if (!RecursionSet.insert(V).second)
570 return false;
571
572 // If V is a constant, then it is known in all predecessors.
573 if (Constant *KC = getKnownConstant(V, Preference)) {
574 for (BasicBlock *Pred : predecessors(BB))
575 Result.emplace_back(KC, Pred);
576
577 return !Result.empty();
578 }
579
580 // If V is a non-instruction value, or an instruction in a different block,
581 // then it can't be derived from a PHI.
582 Instruction *I = dyn_cast<Instruction>(V);
583 if (!I || I->getParent() != BB) {
584
585 // Okay, if this is a live-in value, see if it has a known value at the any
586 // edge from our predecessors.
587 for (BasicBlock *P : predecessors(BB)) {
588 using namespace PatternMatch;
589 // If the value is known by LazyValueInfo to be a constant in a
590 // predecessor, use that information to try to thread this block.
591 Constant *PredCst = LVI->getConstantOnEdge(V, P, BB, CxtI);
592 // If I is a non-local compare-with-constant instruction, use more-rich
593 // 'getPredicateOnEdge' method. This would be able to handle value
594 // inequalities better, for example if the compare is "X < 4" and "X < 3"
595 // is known true but "X < 4" itself is not available.
597 Value *Val;
598 Constant *Cst;
599 if (!PredCst && match(V, m_Cmp(Pred, m_Value(Val), m_Constant(Cst)))) {
600 auto Res = LVI->getPredicateOnEdge(Pred, Val, Cst, P, BB, CxtI);
601 if (Res != LazyValueInfo::Unknown)
602 PredCst = ConstantInt::getBool(V->getContext(), Res);
603 }
604 if (Constant *KC = getKnownConstant(PredCst, Preference))
605 Result.emplace_back(KC, P);
606 }
607
608 return !Result.empty();
609 }
610
611 /// If I is a PHI node, then we know the incoming values for any constants.
612 if (PHINode *PN = dyn_cast<PHINode>(I)) {
613 for (unsigned i = 0, e = PN->getNumIncomingValues(); i != e; ++i) {
614 Value *InVal = PN->getIncomingValue(i);
615 if (Constant *KC = getKnownConstant(InVal, Preference)) {
616 Result.emplace_back(KC, PN->getIncomingBlock(i));
617 } else {
618 Constant *CI = LVI->getConstantOnEdge(InVal,
619 PN->getIncomingBlock(i),
620 BB, CxtI);
621 if (Constant *KC = getKnownConstant(CI, Preference))
622 Result.emplace_back(KC, PN->getIncomingBlock(i));
623 }
624 }
625
626 return !Result.empty();
627 }
628
629 // Handle Cast instructions.
630 if (CastInst *CI = dyn_cast<CastInst>(I)) {
631 Value *Source = CI->getOperand(0);
632 PredValueInfoTy Vals;
633 computeValueKnownInPredecessorsImpl(Source, BB, Vals, Preference,
634 RecursionSet, CxtI);
635 if (Vals.empty())
636 return false;
637
638 // Convert the known values.
639 for (auto &Val : Vals)
640 if (Constant *Folded = ConstantFoldCastOperand(CI->getOpcode(), Val.first,
641 CI->getType(), DL))
642 Result.emplace_back(Folded, Val.second);
643
644 return !Result.empty();
645 }
646
647 if (FreezeInst *FI = dyn_cast<FreezeInst>(I)) {
648 Value *Source = FI->getOperand(0);
649 computeValueKnownInPredecessorsImpl(Source, BB, Result, Preference,
650 RecursionSet, CxtI);
651
652 erase_if(Result, [](auto &Pair) {
653 return !isGuaranteedNotToBeUndefOrPoison(Pair.first);
654 });
655
656 return !Result.empty();
657 }
658
659 // Handle some boolean conditions.
660 if (I->getType()->getPrimitiveSizeInBits() == 1) {
661 using namespace PatternMatch;
662 if (Preference != WantInteger)
663 return false;
664 // X | true -> true
665 // X & false -> false
666 Value *Op0, *Op1;
667 if (match(I, m_LogicalOr(m_Value(Op0), m_Value(Op1))) ||
668 match(I, m_LogicalAnd(m_Value(Op0), m_Value(Op1)))) {
669 PredValueInfoTy LHSVals, RHSVals;
670
672 RecursionSet, CxtI);
674 RecursionSet, CxtI);
675
676 if (LHSVals.empty() && RHSVals.empty())
677 return false;
678
679 ConstantInt *InterestingVal;
680 if (match(I, m_LogicalOr()))
681 InterestingVal = ConstantInt::getTrue(I->getContext());
682 else
683 InterestingVal = ConstantInt::getFalse(I->getContext());
684
685 SmallPtrSet<BasicBlock*, 4> LHSKnownBBs;
686
687 // Scan for the sentinel. If we find an undef, force it to the
688 // interesting value: x|undef -> true and x&undef -> false.
689 for (const auto &LHSVal : LHSVals)
690 if (LHSVal.first == InterestingVal || isa<UndefValue>(LHSVal.first)) {
691 Result.emplace_back(InterestingVal, LHSVal.second);
692 LHSKnownBBs.insert(LHSVal.second);
693 }
694 for (const auto &RHSVal : RHSVals)
695 if (RHSVal.first == InterestingVal || isa<UndefValue>(RHSVal.first)) {
696 // If we already inferred a value for this block on the LHS, don't
697 // re-add it.
698 if (!LHSKnownBBs.count(RHSVal.second))
699 Result.emplace_back(InterestingVal, RHSVal.second);
700 }
701
702 return !Result.empty();
703 }
704
705 // Handle the NOT form of XOR.
706 if (I->getOpcode() == Instruction::Xor &&
707 isa<ConstantInt>(I->getOperand(1)) &&
708 cast<ConstantInt>(I->getOperand(1))->isOne()) {
709 computeValueKnownInPredecessorsImpl(I->getOperand(0), BB, Result,
710 WantInteger, RecursionSet, CxtI);
711 if (Result.empty())
712 return false;
713
714 // Invert the known values.
715 for (auto &R : Result)
716 R.first = ConstantExpr::getNot(R.first);
717
718 return true;
719 }
720
721 // Try to simplify some other binary operator values.
722 } else if (BinaryOperator *BO = dyn_cast<BinaryOperator>(I)) {
723 if (Preference != WantInteger)
724 return false;
725 if (ConstantInt *CI = dyn_cast<ConstantInt>(BO->getOperand(1))) {
726 PredValueInfoTy LHSVals;
727 computeValueKnownInPredecessorsImpl(BO->getOperand(0), BB, LHSVals,
728 WantInteger, RecursionSet, CxtI);
729
730 // Try to use constant folding to simplify the binary operator.
731 for (const auto &LHSVal : LHSVals) {
732 Constant *V = LHSVal.first;
733 Constant *Folded =
734 ConstantFoldBinaryOpOperands(BO->getOpcode(), V, CI, DL);
735
736 if (Constant *KC = getKnownConstant(Folded, WantInteger))
737 Result.emplace_back(KC, LHSVal.second);
738 }
739 }
740
741 return !Result.empty();
742 }
743
744 // Handle compare with phi operand, where the PHI is defined in this block.
745 if (CmpInst *Cmp = dyn_cast<CmpInst>(I)) {
746 if (Preference != WantInteger)
747 return false;
748 Type *CmpType = Cmp->getType();
749 Value *CmpLHS = Cmp->getOperand(0);
750 Value *CmpRHS = Cmp->getOperand(1);
751 CmpInst::Predicate Pred = Cmp->getPredicate();
752
753 PHINode *PN = dyn_cast<PHINode>(CmpLHS);
754 if (!PN)
755 PN = dyn_cast<PHINode>(CmpRHS);
756 // Do not perform phi translation across a loop header phi, because this
757 // may result in comparison of values from two different loop iterations.
758 // FIXME: This check is broken if LoopHeaders is not populated.
759 if (PN && PN->getParent() == BB && !LoopHeaders.contains(BB)) {
760 const DataLayout &DL = PN->getModule()->getDataLayout();
761 // We can do this simplification if any comparisons fold to true or false.
762 // See if any do.
763 for (unsigned i = 0, e = PN->getNumIncomingValues(); i != e; ++i) {
764 BasicBlock *PredBB = PN->getIncomingBlock(i);
765 Value *LHS, *RHS;
766 if (PN == CmpLHS) {
767 LHS = PN->getIncomingValue(i);
768 RHS = CmpRHS->DoPHITranslation(BB, PredBB);
769 } else {
770 LHS = CmpLHS->DoPHITranslation(BB, PredBB);
771 RHS = PN->getIncomingValue(i);
772 }
773 Value *Res = simplifyCmpInst(Pred, LHS, RHS, {DL});
774 if (!Res) {
775 if (!isa<Constant>(RHS))
776 continue;
777
778 // getPredicateOnEdge call will make no sense if LHS is defined in BB.
779 auto LHSInst = dyn_cast<Instruction>(LHS);
780 if (LHSInst && LHSInst->getParent() == BB)
781 continue;
782
784 ResT = LVI->getPredicateOnEdge(Pred, LHS,
785 cast<Constant>(RHS), PredBB, BB,
786 CxtI ? CxtI : Cmp);
787 if (ResT == LazyValueInfo::Unknown)
788 continue;
789 Res = ConstantInt::get(Type::getInt1Ty(LHS->getContext()), ResT);
790 }
791
792 if (Constant *KC = getKnownConstant(Res, WantInteger))
793 Result.emplace_back(KC, PredBB);
794 }
795
796 return !Result.empty();
797 }
798
799 // If comparing a live-in value against a constant, see if we know the
800 // live-in value on any predecessors.
801 if (isa<Constant>(CmpRHS) && !CmpType->isVectorTy()) {
802 Constant *CmpConst = cast<Constant>(CmpRHS);
803
804 if (!isa<Instruction>(CmpLHS) ||
805 cast<Instruction>(CmpLHS)->getParent() != BB) {
806 for (BasicBlock *P : predecessors(BB)) {
807 // If the value is known by LazyValueInfo to be a constant in a
808 // predecessor, use that information to try to thread this block.
810 LVI->getPredicateOnEdge(Pred, CmpLHS,
811 CmpConst, P, BB, CxtI ? CxtI : Cmp);
812 if (Res == LazyValueInfo::Unknown)
813 continue;
814
815 Constant *ResC = ConstantInt::get(CmpType, Res);
816 Result.emplace_back(ResC, P);
817 }
818
819 return !Result.empty();
820 }
821
822 // InstCombine can fold some forms of constant range checks into
823 // (icmp (add (x, C1)), C2). See if we have we have such a thing with
824 // x as a live-in.
825 {
826 using namespace PatternMatch;
827
828 Value *AddLHS;
829 ConstantInt *AddConst;
830 if (isa<ConstantInt>(CmpConst) &&
831 match(CmpLHS, m_Add(m_Value(AddLHS), m_ConstantInt(AddConst)))) {
832 if (!isa<Instruction>(AddLHS) ||
833 cast<Instruction>(AddLHS)->getParent() != BB) {
834 for (BasicBlock *P : predecessors(BB)) {
835 // If the value is known by LazyValueInfo to be a ConstantRange in
836 // a predecessor, use that information to try to thread this
837 // block.
839 AddLHS, P, BB, CxtI ? CxtI : cast<Instruction>(CmpLHS));
840 // Propagate the range through the addition.
841 CR = CR.add(AddConst->getValue());
842
843 // Get the range where the compare returns true.
845 Pred, cast<ConstantInt>(CmpConst)->getValue());
846
847 Constant *ResC;
848 if (CmpRange.contains(CR))
849 ResC = ConstantInt::getTrue(CmpType);
850 else if (CmpRange.inverse().contains(CR))
851 ResC = ConstantInt::getFalse(CmpType);
852 else
853 continue;
854
855 Result.emplace_back(ResC, P);
856 }
857
858 return !Result.empty();
859 }
860 }
861 }
862
863 // Try to find a constant value for the LHS of a comparison,
864 // and evaluate it statically if we can.
865 PredValueInfoTy LHSVals;
866 computeValueKnownInPredecessorsImpl(I->getOperand(0), BB, LHSVals,
867 WantInteger, RecursionSet, CxtI);
868
869 for (const auto &LHSVal : LHSVals) {
870 Constant *V = LHSVal.first;
871 Constant *Folded = ConstantExpr::getCompare(Pred, V, CmpConst);
872 if (Constant *KC = getKnownConstant(Folded, WantInteger))
873 Result.emplace_back(KC, LHSVal.second);
874 }
875
876 return !Result.empty();
877 }
878 }
879
880 if (SelectInst *SI = dyn_cast<SelectInst>(I)) {
881 // Handle select instructions where at least one operand is a known constant
882 // and we can figure out the condition value for any predecessor block.
883 Constant *TrueVal = getKnownConstant(SI->getTrueValue(), Preference);
884 Constant *FalseVal = getKnownConstant(SI->getFalseValue(), Preference);
885 PredValueInfoTy Conds;
886 if ((TrueVal || FalseVal) &&
887 computeValueKnownInPredecessorsImpl(SI->getCondition(), BB, Conds,
888 WantInteger, RecursionSet, CxtI)) {
889 for (auto &C : Conds) {
890 Constant *Cond = C.first;
891
892 // Figure out what value to use for the condition.
893 bool KnownCond;
894 if (ConstantInt *CI = dyn_cast<ConstantInt>(Cond)) {
895 // A known boolean.
896 KnownCond = CI->isOne();
897 } else {
898 assert(isa<UndefValue>(Cond) && "Unexpected condition value");
899 // Either operand will do, so be sure to pick the one that's a known
900 // constant.
901 // FIXME: Do this more cleverly if both values are known constants?
902 KnownCond = (TrueVal != nullptr);
903 }
904
905 // See if the select has a known constant value for this predecessor.
906 if (Constant *Val = KnownCond ? TrueVal : FalseVal)
907 Result.emplace_back(Val, C.second);
908 }
909
910 return !Result.empty();
911 }
912 }
913
914 // If all else fails, see if LVI can figure out a constant value for us.
915 assert(CxtI->getParent() == BB && "CxtI should be in BB");
916 Constant *CI = LVI->getConstant(V, CxtI);
917 if (Constant *KC = getKnownConstant(CI, Preference)) {
918 for (BasicBlock *Pred : predecessors(BB))
919 Result.emplace_back(KC, Pred);
920 }
921
922 return !Result.empty();
923}
924
925/// GetBestDestForBranchOnUndef - If we determine that the specified block ends
926/// in an undefined jump, decide which block is best to revector to.
927///
928/// Since we can pick an arbitrary destination, we pick the successor with the
929/// fewest predecessors. This should reduce the in-degree of the others.
931 Instruction *BBTerm = BB->getTerminator();
932 unsigned MinSucc = 0;
933 BasicBlock *TestBB = BBTerm->getSuccessor(MinSucc);
934 // Compute the successor with the minimum number of predecessors.
935 unsigned MinNumPreds = pred_size(TestBB);
936 for (unsigned i = 1, e = BBTerm->getNumSuccessors(); i != e; ++i) {
937 TestBB = BBTerm->getSuccessor(i);
938 unsigned NumPreds = pred_size(TestBB);
939 if (NumPreds < MinNumPreds) {
940 MinSucc = i;
941 MinNumPreds = NumPreds;
942 }
943 }
944
945 return MinSucc;
946}
947
949 if (!BB->hasAddressTaken()) return false;
950
951 // If the block has its address taken, it may be a tree of dead constants
952 // hanging off of it. These shouldn't keep the block alive.
955 return !BA->use_empty();
956}
957
958/// processBlock - If there are any predecessors whose control can be threaded
959/// through to a successor, transform them now.
961 // If the block is trivially dead, just return and let the caller nuke it.
962 // This simplifies other transformations.
963 if (DTU->isBBPendingDeletion(BB) ||
964 (pred_empty(BB) && BB != &BB->getParent()->getEntryBlock()))
965 return false;
966
967 // If this block has a single predecessor, and if that pred has a single
968 // successor, merge the blocks. This encourages recursive jump threading
969 // because now the condition in this block can be threaded through
970 // predecessors of our predecessor block.
972 return true;
973
975 return true;
976
977 // Look if we can propagate guards to predecessors.
978 if (HasGuards && processGuards(BB))
979 return true;
980
981 // What kind of constant we're looking for.
982 ConstantPreference Preference = WantInteger;
983
984 // Look to see if the terminator is a conditional branch, switch or indirect
985 // branch, if not we can't thread it.
986 Value *Condition;
987 Instruction *Terminator = BB->getTerminator();
988 if (BranchInst *BI = dyn_cast<BranchInst>(Terminator)) {
989 // Can't thread an unconditional jump.
990 if (BI->isUnconditional()) return false;
991 Condition = BI->getCondition();
992 } else if (SwitchInst *SI = dyn_cast<SwitchInst>(Terminator)) {
993 Condition = SI->getCondition();
994 } else if (IndirectBrInst *IB = dyn_cast<IndirectBrInst>(Terminator)) {
995 // Can't thread indirect branch with no successors.
996 if (IB->getNumSuccessors() == 0) return false;
997 Condition = IB->getAddress()->stripPointerCasts();
998 Preference = WantBlockAddress;
999 } else {
1000 return false; // Must be an invoke or callbr.
1001 }
1002
1003 // Keep track if we constant folded the condition in this invocation.
1004 bool ConstantFolded = false;
1005
1006 // Run constant folding to see if we can reduce the condition to a simple
1007 // constant.
1008 if (Instruction *I = dyn_cast<Instruction>(Condition)) {
1009 Value *SimpleVal =
1011 if (SimpleVal) {
1012 I->replaceAllUsesWith(SimpleVal);
1013 if (isInstructionTriviallyDead(I, TLI))
1014 I->eraseFromParent();
1015 Condition = SimpleVal;
1016 ConstantFolded = true;
1017 }
1018 }
1019
1020 // If the terminator is branching on an undef or freeze undef, we can pick any
1021 // of the successors to branch to. Let getBestDestForJumpOnUndef decide.
1022 auto *FI = dyn_cast<FreezeInst>(Condition);
1023 if (isa<UndefValue>(Condition) ||
1024 (FI && isa<UndefValue>(FI->getOperand(0)) && FI->hasOneUse())) {
1025 unsigned BestSucc = getBestDestForJumpOnUndef(BB);
1026 std::vector<DominatorTree::UpdateType> Updates;
1027
1028 // Fold the branch/switch.
1029 Instruction *BBTerm = BB->getTerminator();
1030 Updates.reserve(BBTerm->getNumSuccessors());
1031 for (unsigned i = 0, e = BBTerm->getNumSuccessors(); i != e; ++i) {
1032 if (i == BestSucc) continue;
1033 BasicBlock *Succ = BBTerm->getSuccessor(i);
1034 Succ->removePredecessor(BB, true);
1035 Updates.push_back({DominatorTree::Delete, BB, Succ});
1036 }
1037
1038 LLVM_DEBUG(dbgs() << " In block '" << BB->getName()
1039 << "' folding undef terminator: " << *BBTerm << '\n');
1040 BranchInst::Create(BBTerm->getSuccessor(BestSucc), BBTerm->getIterator());
1041 ++NumFolds;
1042 BBTerm->eraseFromParent();
1043 DTU->applyUpdatesPermissive(Updates);
1044 if (FI)
1045 FI->eraseFromParent();
1046 return true;
1047 }
1048
1049 // If the terminator of this block is branching on a constant, simplify the
1050 // terminator to an unconditional branch. This can occur due to threading in
1051 // other blocks.
1052 if (getKnownConstant(Condition, Preference)) {
1053 LLVM_DEBUG(dbgs() << " In block '" << BB->getName()
1054 << "' folding terminator: " << *BB->getTerminator()
1055 << '\n');
1056 ++NumFolds;
1057 ConstantFoldTerminator(BB, true, nullptr, DTU.get());
1058 if (auto *BPI = getBPI())
1059 BPI->eraseBlock(BB);
1060 return true;
1061 }
1062
1063 Instruction *CondInst = dyn_cast<Instruction>(Condition);
1064
1065 // All the rest of our checks depend on the condition being an instruction.
1066 if (!CondInst) {
1067 // FIXME: Unify this with code below.
1068 if (processThreadableEdges(Condition, BB, Preference, Terminator))
1069 return true;
1070 return ConstantFolded;
1071 }
1072
1073 // Some of the following optimization can safely work on the unfrozen cond.
1074 Value *CondWithoutFreeze = CondInst;
1075 if (auto *FI = dyn_cast<FreezeInst>(CondInst))
1076 CondWithoutFreeze = FI->getOperand(0);
1077
1078 if (CmpInst *CondCmp = dyn_cast<CmpInst>(CondWithoutFreeze)) {
1079 // If we're branching on a conditional, LVI might be able to determine
1080 // it's value at the branch instruction. We only handle comparisons
1081 // against a constant at this time.
1082 if (Constant *CondConst = dyn_cast<Constant>(CondCmp->getOperand(1))) {
1084 LVI->getPredicateAt(CondCmp->getPredicate(), CondCmp->getOperand(0),
1085 CondConst, BB->getTerminator(),
1086 /*UseBlockValue=*/false);
1087 if (Ret != LazyValueInfo::Unknown) {
1088 // We can safely replace *some* uses of the CondInst if it has
1089 // exactly one value as returned by LVI. RAUW is incorrect in the
1090 // presence of guards and assumes, that have the `Cond` as the use. This
1091 // is because we use the guards/assume to reason about the `Cond` value
1092 // at the end of block, but RAUW unconditionally replaces all uses
1093 // including the guards/assumes themselves and the uses before the
1094 // guard/assume.
1095 auto *CI = Ret == LazyValueInfo::True ?
1096 ConstantInt::getTrue(CondCmp->getType()) :
1097 ConstantInt::getFalse(CondCmp->getType());
1098 if (replaceFoldableUses(CondCmp, CI, BB))
1099 return true;
1100 }
1101
1102 // We did not manage to simplify this branch, try to see whether
1103 // CondCmp depends on a known phi-select pattern.
1104 if (tryToUnfoldSelect(CondCmp, BB))
1105 return true;
1106 }
1107 }
1108
1109 if (SwitchInst *SI = dyn_cast<SwitchInst>(BB->getTerminator()))
1110 if (tryToUnfoldSelect(SI, BB))
1111 return true;
1112
1113 // Check for some cases that are worth simplifying. Right now we want to look
1114 // for loads that are used by a switch or by the condition for the branch. If
1115 // we see one, check to see if it's partially redundant. If so, insert a PHI
1116 // which can then be used to thread the values.
1117 Value *SimplifyValue = CondWithoutFreeze;
1118
1119 if (CmpInst *CondCmp = dyn_cast<CmpInst>(SimplifyValue))
1120 if (isa<Constant>(CondCmp->getOperand(1)))
1121 SimplifyValue = CondCmp->getOperand(0);
1122
1123 // TODO: There are other places where load PRE would be profitable, such as
1124 // more complex comparisons.
1125 if (LoadInst *LoadI = dyn_cast<LoadInst>(SimplifyValue))
1127 return true;
1128
1129 // Before threading, try to propagate profile data backwards:
1130 if (PHINode *PN = dyn_cast<PHINode>(CondInst))
1131 if (PN->getParent() == BB && isa<BranchInst>(BB->getTerminator()))
1133
1134 // Handle a variety of cases where we are branching on something derived from
1135 // a PHI node in the current block. If we can prove that any predecessors
1136 // compute a predictable value based on a PHI node, thread those predecessors.
1137 if (processThreadableEdges(CondInst, BB, Preference, Terminator))
1138 return true;
1139
1140 // If this is an otherwise-unfoldable branch on a phi node or freeze(phi) in
1141 // the current block, see if we can simplify.
1142 PHINode *PN = dyn_cast<PHINode>(CondWithoutFreeze);
1143 if (PN && PN->getParent() == BB && isa<BranchInst>(BB->getTerminator()))
1144 return processBranchOnPHI(PN);
1145
1146 // If this is an otherwise-unfoldable branch on a XOR, see if we can simplify.
1147 if (CondInst->getOpcode() == Instruction::Xor &&
1148 CondInst->getParent() == BB && isa<BranchInst>(BB->getTerminator()))
1149 return processBranchOnXOR(cast<BinaryOperator>(CondInst));
1150
1151 // Search for a stronger dominating condition that can be used to simplify a
1152 // conditional branch leaving BB.
1154 return true;
1155
1156 return false;
1157}
1158
1160 auto *BI = dyn_cast<BranchInst>(BB->getTerminator());
1161 if (!BI || !BI->isConditional())
1162 return false;
1163
1164 Value *Cond = BI->getCondition();
1165 // Assuming that predecessor's branch was taken, if pred's branch condition
1166 // (V) implies Cond, Cond can be either true, undef, or poison. In this case,
1167 // freeze(Cond) is either true or a nondeterministic value.
1168 // If freeze(Cond) has only one use, we can freely fold freeze(Cond) to true
1169 // without affecting other instructions.
1170 auto *FICond = dyn_cast<FreezeInst>(Cond);
1171 if (FICond && FICond->hasOneUse())
1172 Cond = FICond->getOperand(0);
1173 else
1174 FICond = nullptr;
1175
1176 BasicBlock *CurrentBB = BB;
1177 BasicBlock *CurrentPred = BB->getSinglePredecessor();
1178 unsigned Iter = 0;
1179
1180 auto &DL = BB->getModule()->getDataLayout();
1181
1182 while (CurrentPred && Iter++ < ImplicationSearchThreshold) {
1183 auto *PBI = dyn_cast<BranchInst>(CurrentPred->getTerminator());
1184 if (!PBI || !PBI->isConditional())
1185 return false;
1186 if (PBI->getSuccessor(0) != CurrentBB && PBI->getSuccessor(1) != CurrentBB)
1187 return false;
1188
1189 bool CondIsTrue = PBI->getSuccessor(0) == CurrentBB;
1190 std::optional<bool> Implication =
1191 isImpliedCondition(PBI->getCondition(), Cond, DL, CondIsTrue);
1192
1193 // If the branch condition of BB (which is Cond) and CurrentPred are
1194 // exactly the same freeze instruction, Cond can be folded into CondIsTrue.
1195 if (!Implication && FICond && isa<FreezeInst>(PBI->getCondition())) {
1196 if (cast<FreezeInst>(PBI->getCondition())->getOperand(0) ==
1197 FICond->getOperand(0))
1198 Implication = CondIsTrue;
1199 }
1200
1201 if (Implication) {
1202 BasicBlock *KeepSucc = BI->getSuccessor(*Implication ? 0 : 1);
1203 BasicBlock *RemoveSucc = BI->getSuccessor(*Implication ? 1 : 0);
1204 RemoveSucc->removePredecessor(BB);
1205 BranchInst *UncondBI = BranchInst::Create(KeepSucc, BI->getIterator());
1206 UncondBI->setDebugLoc(BI->getDebugLoc());
1207 ++NumFolds;
1208 BI->eraseFromParent();
1209 if (FICond)
1210 FICond->eraseFromParent();
1211
1212 DTU->applyUpdatesPermissive({{DominatorTree::Delete, BB, RemoveSucc}});
1213 if (auto *BPI = getBPI())
1214 BPI->eraseBlock(BB);
1215 return true;
1216 }
1217 CurrentBB = CurrentPred;
1218 CurrentPred = CurrentBB->getSinglePredecessor();
1219 }
1220
1221 return false;
1222}
1223
1224/// Return true if Op is an instruction defined in the given block.
1226 if (Instruction *OpInst = dyn_cast<Instruction>(Op))
1227 if (OpInst->getParent() == BB)
1228 return true;
1229 return false;
1230}
1231
1232/// simplifyPartiallyRedundantLoad - If LoadI is an obviously partially
1233/// redundant load instruction, eliminate it by replacing it with a PHI node.
1234/// This is an important optimization that encourages jump threading, and needs
1235/// to be run interlaced with other jump threading tasks.
1237 // Don't hack volatile and ordered loads.
1238 if (!LoadI->isUnordered()) return false;
1239
1240 // If the load is defined in a block with exactly one predecessor, it can't be
1241 // partially redundant.
1242 BasicBlock *LoadBB = LoadI->getParent();
1243 if (LoadBB->getSinglePredecessor())
1244 return false;
1245
1246 // If the load is defined in an EH pad, it can't be partially redundant,
1247 // because the edges between the invoke and the EH pad cannot have other
1248 // instructions between them.
1249 if (LoadBB->isEHPad())
1250 return false;
1251
1252 Value *LoadedPtr = LoadI->getOperand(0);
1253
1254 // If the loaded operand is defined in the LoadBB and its not a phi,
1255 // it can't be available in predecessors.
1256 if (isOpDefinedInBlock(LoadedPtr, LoadBB) && !isa<PHINode>(LoadedPtr))
1257 return false;
1258
1259 // Scan a few instructions up from the load, to see if it is obviously live at
1260 // the entry to its block.
1261 BasicBlock::iterator BBIt(LoadI);
1262 bool IsLoadCSE;
1263 BatchAAResults BatchAA(*AA);
1264 // The dominator tree is updated lazily and may not be valid at this point.
1265 BatchAA.disableDominatorTree();
1266 if (Value *AvailableVal = FindAvailableLoadedValue(
1267 LoadI, LoadBB, BBIt, DefMaxInstsToScan, &BatchAA, &IsLoadCSE)) {
1268 // If the value of the load is locally available within the block, just use
1269 // it. This frequently occurs for reg2mem'd allocas.
1270
1271 if (IsLoadCSE) {
1272 LoadInst *NLoadI = cast<LoadInst>(AvailableVal);
1273 combineMetadataForCSE(NLoadI, LoadI, false);
1274 LVI->forgetValue(NLoadI);
1275 };
1276
1277 // If the returned value is the load itself, replace with poison. This can
1278 // only happen in dead loops.
1279 if (AvailableVal == LoadI)
1280 AvailableVal = PoisonValue::get(LoadI->getType());
1281 if (AvailableVal->getType() != LoadI->getType())
1282 AvailableVal = CastInst::CreateBitOrPointerCast(
1283 AvailableVal, LoadI->getType(), "", LoadI->getIterator());
1284 LoadI->replaceAllUsesWith(AvailableVal);
1285 LoadI->eraseFromParent();
1286 return true;
1287 }
1288
1289 // Otherwise, if we scanned the whole block and got to the top of the block,
1290 // we know the block is locally transparent to the load. If not, something
1291 // might clobber its value.
1292 if (BBIt != LoadBB->begin())
1293 return false;
1294
1295 // If all of the loads and stores that feed the value have the same AA tags,
1296 // then we can propagate them onto any newly inserted loads.
1297 AAMDNodes AATags = LoadI->getAAMetadata();
1298
1299 SmallPtrSet<BasicBlock*, 8> PredsScanned;
1300
1301 using AvailablePredsTy = SmallVector<std::pair<BasicBlock *, Value *>, 8>;
1302
1303 AvailablePredsTy AvailablePreds;
1304 BasicBlock *OneUnavailablePred = nullptr;
1306
1307 // If we got here, the loaded value is transparent through to the start of the
1308 // block. Check to see if it is available in any of the predecessor blocks.
1309 for (BasicBlock *PredBB : predecessors(LoadBB)) {
1310 // If we already scanned this predecessor, skip it.
1311 if (!PredsScanned.insert(PredBB).second)
1312 continue;
1313
1314 BBIt = PredBB->end();
1315 unsigned NumScanedInst = 0;
1316 Value *PredAvailable = nullptr;
1317 // NOTE: We don't CSE load that is volatile or anything stronger than
1318 // unordered, that should have been checked when we entered the function.
1319 assert(LoadI->isUnordered() &&
1320 "Attempting to CSE volatile or atomic loads");
1321 // If this is a load on a phi pointer, phi-translate it and search
1322 // for available load/store to the pointer in predecessors.
1323 Type *AccessTy = LoadI->getType();
1324 const auto &DL = LoadI->getModule()->getDataLayout();
1325 MemoryLocation Loc(LoadedPtr->DoPHITranslation(LoadBB, PredBB),
1326 LocationSize::precise(DL.getTypeStoreSize(AccessTy)),
1327 AATags);
1328 PredAvailable = findAvailablePtrLoadStore(
1329 Loc, AccessTy, LoadI->isAtomic(), PredBB, BBIt, DefMaxInstsToScan,
1330 &BatchAA, &IsLoadCSE, &NumScanedInst);
1331
1332 // If PredBB has a single predecessor, continue scanning through the
1333 // single predecessor.
1334 BasicBlock *SinglePredBB = PredBB;
1335 while (!PredAvailable && SinglePredBB && BBIt == SinglePredBB->begin() &&
1336 NumScanedInst < DefMaxInstsToScan) {
1337 SinglePredBB = SinglePredBB->getSinglePredecessor();
1338 if (SinglePredBB) {
1339 BBIt = SinglePredBB->end();
1340 PredAvailable = findAvailablePtrLoadStore(
1341 Loc, AccessTy, LoadI->isAtomic(), SinglePredBB, BBIt,
1342 (DefMaxInstsToScan - NumScanedInst), &BatchAA, &IsLoadCSE,
1343 &NumScanedInst);
1344 }
1345 }
1346
1347 if (!PredAvailable) {
1348 OneUnavailablePred = PredBB;
1349 continue;
1350 }
1351
1352 if (IsLoadCSE)
1353 CSELoads.push_back(cast<LoadInst>(PredAvailable));
1354
1355 // If so, this load is partially redundant. Remember this info so that we
1356 // can create a PHI node.
1357 AvailablePreds.emplace_back(PredBB, PredAvailable);
1358 }
1359
1360 // If the loaded value isn't available in any predecessor, it isn't partially
1361 // redundant.
1362 if (AvailablePreds.empty()) return false;
1363
1364 // Okay, the loaded value is available in at least one (and maybe all!)
1365 // predecessors. If the value is unavailable in more than one unique
1366 // predecessor, we want to insert a merge block for those common predecessors.
1367 // This ensures that we only have to insert one reload, thus not increasing
1368 // code size.
1369 BasicBlock *UnavailablePred = nullptr;
1370
1371 // If the value is unavailable in one of predecessors, we will end up
1372 // inserting a new instruction into them. It is only valid if all the
1373 // instructions before LoadI are guaranteed to pass execution to its
1374 // successor, or if LoadI is safe to speculate.
1375 // TODO: If this logic becomes more complex, and we will perform PRE insertion
1376 // farther than to a predecessor, we need to reuse the code from GVN's PRE.
1377 // It requires domination tree analysis, so for this simple case it is an
1378 // overkill.
1379 if (PredsScanned.size() != AvailablePreds.size() &&
1381 for (auto I = LoadBB->begin(); &*I != LoadI; ++I)
1383 return false;
1384
1385 // If there is exactly one predecessor where the value is unavailable, the
1386 // already computed 'OneUnavailablePred' block is it. If it ends in an
1387 // unconditional branch, we know that it isn't a critical edge.
1388 if (PredsScanned.size() == AvailablePreds.size()+1 &&
1389 OneUnavailablePred->getTerminator()->getNumSuccessors() == 1) {
1390 UnavailablePred = OneUnavailablePred;
1391 } else if (PredsScanned.size() != AvailablePreds.size()) {
1392 // Otherwise, we had multiple unavailable predecessors or we had a critical
1393 // edge from the one.
1394 SmallVector<BasicBlock*, 8> PredsToSplit;
1395 SmallPtrSet<BasicBlock*, 8> AvailablePredSet;
1396
1397 for (const auto &AvailablePred : AvailablePreds)
1398 AvailablePredSet.insert(AvailablePred.first);
1399
1400 // Add all the unavailable predecessors to the PredsToSplit list.
1401 for (BasicBlock *P : predecessors(LoadBB)) {
1402 // If the predecessor is an indirect goto, we can't split the edge.
1403 if (isa<IndirectBrInst>(P->getTerminator()))
1404 return false;
1405
1406 if (!AvailablePredSet.count(P))
1407 PredsToSplit.push_back(P);
1408 }
1409
1410 // Split them out to their own block.
1411 UnavailablePred = splitBlockPreds(LoadBB, PredsToSplit, "thread-pre-split");
1412 }
1413
1414 // If the value isn't available in all predecessors, then there will be
1415 // exactly one where it isn't available. Insert a load on that edge and add
1416 // it to the AvailablePreds list.
1417 if (UnavailablePred) {
1418 assert(UnavailablePred->getTerminator()->getNumSuccessors() == 1 &&
1419 "Can't handle critical edge here!");
1420 LoadInst *NewVal = new LoadInst(
1421 LoadI->getType(), LoadedPtr->DoPHITranslation(LoadBB, UnavailablePred),
1422 LoadI->getName() + ".pr", false, LoadI->getAlign(),
1423 LoadI->getOrdering(), LoadI->getSyncScopeID(),
1424 UnavailablePred->getTerminator()->getIterator());
1425 NewVal->setDebugLoc(LoadI->getDebugLoc());
1426 if (AATags)
1427 NewVal->setAAMetadata(AATags);
1428
1429 AvailablePreds.emplace_back(UnavailablePred, NewVal);
1430 }
1431
1432 // Now we know that each predecessor of this block has a value in
1433 // AvailablePreds, sort them for efficient access as we're walking the preds.
1434 array_pod_sort(AvailablePreds.begin(), AvailablePreds.end());
1435
1436 // Create a PHI node at the start of the block for the PRE'd load value.
1437 PHINode *PN = PHINode::Create(LoadI->getType(), pred_size(LoadBB), "");
1438 PN->insertBefore(LoadBB->begin());
1439 PN->takeName(LoadI);
1440 PN->setDebugLoc(LoadI->getDebugLoc());
1441
1442 // Insert new entries into the PHI for each predecessor. A single block may
1443 // have multiple entries here.
1444 for (BasicBlock *P : predecessors(LoadBB)) {
1445 AvailablePredsTy::iterator I =
1446 llvm::lower_bound(AvailablePreds, std::make_pair(P, (Value *)nullptr));
1447
1448 assert(I != AvailablePreds.end() && I->first == P &&
1449 "Didn't find entry for predecessor!");
1450
1451 // If we have an available predecessor but it requires casting, insert the
1452 // cast in the predecessor and use the cast. Note that we have to update the
1453 // AvailablePreds vector as we go so that all of the PHI entries for this
1454 // predecessor use the same bitcast.
1455 Value *&PredV = I->second;
1456 if (PredV->getType() != LoadI->getType())
1458 PredV, LoadI->getType(), "", P->getTerminator()->getIterator());
1459
1460 PN->addIncoming(PredV, I->first);
1461 }
1462
1463 for (LoadInst *PredLoadI : CSELoads) {
1464 combineMetadataForCSE(PredLoadI, LoadI, true);
1465 LVI->forgetValue(PredLoadI);
1466 }
1467
1468 LoadI->replaceAllUsesWith(PN);
1469 LoadI->eraseFromParent();
1470
1471 return true;
1472}
1473
1474/// findMostPopularDest - The specified list contains multiple possible
1475/// threadable destinations. Pick the one that occurs the most frequently in
1476/// the list.
1477static BasicBlock *
1479 const SmallVectorImpl<std::pair<BasicBlock *,
1480 BasicBlock *>> &PredToDestList) {
1481 assert(!PredToDestList.empty());
1482
1483 // Determine popularity. If there are multiple possible destinations, we
1484 // explicitly choose to ignore 'undef' destinations. We prefer to thread
1485 // blocks with known and real destinations to threading undef. We'll handle
1486 // them later if interesting.
1487 MapVector<BasicBlock *, unsigned> DestPopularity;
1488
1489 // Populate DestPopularity with the successors in the order they appear in the
1490 // successor list. This way, we ensure determinism by iterating it in the
1491 // same order in llvm::max_element below. We map nullptr to 0 so that we can
1492 // return nullptr when PredToDestList contains nullptr only.
1493 DestPopularity[nullptr] = 0;
1494 for (auto *SuccBB : successors(BB))
1495 DestPopularity[SuccBB] = 0;
1496
1497 for (const auto &PredToDest : PredToDestList)
1498 if (PredToDest.second)
1499 DestPopularity[PredToDest.second]++;
1500
1501 // Find the most popular dest.
1502 auto MostPopular = llvm::max_element(DestPopularity, llvm::less_second());
1503
1504 // Okay, we have finally picked the most popular destination.
1505 return MostPopular->first;
1506}
1507
1508// Try to evaluate the value of V when the control flows from PredPredBB to
1509// BB->getSinglePredecessor() and then on to BB.
1511 BasicBlock *PredPredBB,
1512 Value *V) {
1513 BasicBlock *PredBB = BB->getSinglePredecessor();
1514 assert(PredBB && "Expected a single predecessor");
1515
1516 if (Constant *Cst = dyn_cast<Constant>(V)) {
1517 return Cst;
1518 }
1519
1520 // Consult LVI if V is not an instruction in BB or PredBB.
1521 Instruction *I = dyn_cast<Instruction>(V);
1522 if (!I || (I->getParent() != BB && I->getParent() != PredBB)) {
1523 return LVI->getConstantOnEdge(V, PredPredBB, PredBB, nullptr);
1524 }
1525
1526 // Look into a PHI argument.
1527 if (PHINode *PHI = dyn_cast<PHINode>(V)) {
1528 if (PHI->getParent() == PredBB)
1529 return dyn_cast<Constant>(PHI->getIncomingValueForBlock(PredPredBB));
1530 return nullptr;
1531 }
1532
1533 // If we have a CmpInst, try to fold it for each incoming edge into PredBB.
1534 if (CmpInst *CondCmp = dyn_cast<CmpInst>(V)) {
1535 if (CondCmp->getParent() == BB) {
1536 Constant *Op0 =
1537 evaluateOnPredecessorEdge(BB, PredPredBB, CondCmp->getOperand(0));
1538 Constant *Op1 =
1539 evaluateOnPredecessorEdge(BB, PredPredBB, CondCmp->getOperand(1));
1540 if (Op0 && Op1) {
1541 return ConstantExpr::getCompare(CondCmp->getPredicate(), Op0, Op1);
1542 }
1543 }
1544 return nullptr;
1545 }
1546
1547 return nullptr;
1548}
1549
1551 ConstantPreference Preference,
1552 Instruction *CxtI) {
1553 // If threading this would thread across a loop header, don't even try to
1554 // thread the edge.
1555 if (LoopHeaders.count(BB))
1556 return false;
1557
1558 PredValueInfoTy PredValues;
1559 if (!computeValueKnownInPredecessors(Cond, BB, PredValues, Preference,
1560 CxtI)) {
1561 // We don't have known values in predecessors. See if we can thread through
1562 // BB and its sole predecessor.
1564 }
1565
1566 assert(!PredValues.empty() &&
1567 "computeValueKnownInPredecessors returned true with no values");
1568
1569 LLVM_DEBUG(dbgs() << "IN BB: " << *BB;
1570 for (const auto &PredValue : PredValues) {
1571 dbgs() << " BB '" << BB->getName()
1572 << "': FOUND condition = " << *PredValue.first
1573 << " for pred '" << PredValue.second->getName() << "'.\n";
1574 });
1575
1576 // Decide what we want to thread through. Convert our list of known values to
1577 // a list of known destinations for each pred. This also discards duplicate
1578 // predecessors and keeps track of the undefined inputs (which are represented
1579 // as a null dest in the PredToDestList).
1582
1583 BasicBlock *OnlyDest = nullptr;
1584 BasicBlock *MultipleDestSentinel = (BasicBlock*)(intptr_t)~0ULL;
1585 Constant *OnlyVal = nullptr;
1586 Constant *MultipleVal = (Constant *)(intptr_t)~0ULL;
1587
1588 for (const auto &PredValue : PredValues) {
1589 BasicBlock *Pred = PredValue.second;
1590 if (!SeenPreds.insert(Pred).second)
1591 continue; // Duplicate predecessor entry.
1592
1593 Constant *Val = PredValue.first;
1594
1595 BasicBlock *DestBB;
1596 if (isa<UndefValue>(Val))
1597 DestBB = nullptr;
1598 else if (BranchInst *BI = dyn_cast<BranchInst>(BB->getTerminator())) {
1599 assert(isa<ConstantInt>(Val) && "Expecting a constant integer");
1600 DestBB = BI->getSuccessor(cast<ConstantInt>(Val)->isZero());
1601 } else if (SwitchInst *SI = dyn_cast<SwitchInst>(BB->getTerminator())) {
1602 assert(isa<ConstantInt>(Val) && "Expecting a constant integer");
1603 DestBB = SI->findCaseValue(cast<ConstantInt>(Val))->getCaseSuccessor();
1604 } else {
1605 assert(isa<IndirectBrInst>(BB->getTerminator())
1606 && "Unexpected terminator");
1607 assert(isa<BlockAddress>(Val) && "Expecting a constant blockaddress");
1608 DestBB = cast<BlockAddress>(Val)->getBasicBlock();
1609 }
1610
1611 // If we have exactly one destination, remember it for efficiency below.
1612 if (PredToDestList.empty()) {
1613 OnlyDest = DestBB;
1614 OnlyVal = Val;
1615 } else {
1616 if (OnlyDest != DestBB)
1617 OnlyDest = MultipleDestSentinel;
1618 // It possible we have same destination, but different value, e.g. default
1619 // case in switchinst.
1620 if (Val != OnlyVal)
1621 OnlyVal = MultipleVal;
1622 }
1623
1624 // If the predecessor ends with an indirect goto, we can't change its
1625 // destination.
1626 if (isa<IndirectBrInst>(Pred->getTerminator()))
1627 continue;
1628
1629 PredToDestList.emplace_back(Pred, DestBB);
1630 }
1631
1632 // If all edges were unthreadable, we fail.
1633 if (PredToDestList.empty())
1634 return false;
1635
1636 // If all the predecessors go to a single known successor, we want to fold,
1637 // not thread. By doing so, we do not need to duplicate the current block and
1638 // also miss potential opportunities in case we dont/cant duplicate.
1639 if (OnlyDest && OnlyDest != MultipleDestSentinel) {
1640 if (BB->hasNPredecessors(PredToDestList.size())) {
1641 bool SeenFirstBranchToOnlyDest = false;
1642 std::vector <DominatorTree::UpdateType> Updates;
1643 Updates.reserve(BB->getTerminator()->getNumSuccessors() - 1);
1644 for (BasicBlock *SuccBB : successors(BB)) {
1645 if (SuccBB == OnlyDest && !SeenFirstBranchToOnlyDest) {
1646 SeenFirstBranchToOnlyDest = true; // Don't modify the first branch.
1647 } else {
1648 SuccBB->removePredecessor(BB, true); // This is unreachable successor.
1649 Updates.push_back({DominatorTree::Delete, BB, SuccBB});
1650 }
1651 }
1652
1653 // Finally update the terminator.
1654 Instruction *Term = BB->getTerminator();
1655 BranchInst::Create(OnlyDest, Term->getIterator());
1656 ++NumFolds;
1657 Term->eraseFromParent();
1658 DTU->applyUpdatesPermissive(Updates);
1659 if (auto *BPI = getBPI())
1660 BPI->eraseBlock(BB);
1661
1662 // If the condition is now dead due to the removal of the old terminator,
1663 // erase it.
1664 if (auto *CondInst = dyn_cast<Instruction>(Cond)) {
1665 if (CondInst->use_empty() && !CondInst->mayHaveSideEffects())
1666 CondInst->eraseFromParent();
1667 // We can safely replace *some* uses of the CondInst if it has
1668 // exactly one value as returned by LVI. RAUW is incorrect in the
1669 // presence of guards and assumes, that have the `Cond` as the use. This
1670 // is because we use the guards/assume to reason about the `Cond` value
1671 // at the end of block, but RAUW unconditionally replaces all uses
1672 // including the guards/assumes themselves and the uses before the
1673 // guard/assume.
1674 else if (OnlyVal && OnlyVal != MultipleVal)
1675 replaceFoldableUses(CondInst, OnlyVal, BB);
1676 }
1677 return true;
1678 }
1679 }
1680
1681 // Determine which is the most common successor. If we have many inputs and
1682 // this block is a switch, we want to start by threading the batch that goes
1683 // to the most popular destination first. If we only know about one
1684 // threadable destination (the common case) we can avoid this.
1685 BasicBlock *MostPopularDest = OnlyDest;
1686
1687 if (MostPopularDest == MultipleDestSentinel) {
1688 // Remove any loop headers from the Dest list, threadEdge conservatively
1689 // won't process them, but we might have other destination that are eligible
1690 // and we still want to process.
1691 erase_if(PredToDestList,
1692 [&](const std::pair<BasicBlock *, BasicBlock *> &PredToDest) {
1693 return LoopHeaders.contains(PredToDest.second);
1694 });
1695
1696 if (PredToDestList.empty())
1697 return false;
1698
1699 MostPopularDest = findMostPopularDest(BB, PredToDestList);
1700 }
1701
1702 // Now that we know what the most popular destination is, factor all
1703 // predecessors that will jump to it into a single predecessor.
1704 SmallVector<BasicBlock*, 16> PredsToFactor;
1705 for (const auto &PredToDest : PredToDestList)
1706 if (PredToDest.second == MostPopularDest) {
1707 BasicBlock *Pred = PredToDest.first;
1708
1709 // This predecessor may be a switch or something else that has multiple
1710 // edges to the block. Factor each of these edges by listing them
1711 // according to # occurrences in PredsToFactor.
1712 for (BasicBlock *Succ : successors(Pred))
1713 if (Succ == BB)
1714 PredsToFactor.push_back(Pred);
1715 }
1716
1717 // If the threadable edges are branching on an undefined value, we get to pick
1718 // the destination that these predecessors should get to.
1719 if (!MostPopularDest)
1720 MostPopularDest = BB->getTerminator()->
1721 getSuccessor(getBestDestForJumpOnUndef(BB));
1722
1723 // Ok, try to thread it!
1724 return tryThreadEdge(BB, PredsToFactor, MostPopularDest);
1725}
1726
1727/// processBranchOnPHI - We have an otherwise unthreadable conditional branch on
1728/// a PHI node (or freeze PHI) in the current block. See if there are any
1729/// simplifications we can do based on inputs to the phi node.
1731 BasicBlock *BB = PN->getParent();
1732
1733 // TODO: We could make use of this to do it once for blocks with common PHI
1734 // values.
1736 PredBBs.resize(1);
1737
1738 // If any of the predecessor blocks end in an unconditional branch, we can
1739 // *duplicate* the conditional branch into that block in order to further
1740 // encourage jump threading and to eliminate cases where we have branch on a
1741 // phi of an icmp (branch on icmp is much better).
1742 // This is still beneficial when a frozen phi is used as the branch condition
1743 // because it allows CodeGenPrepare to further canonicalize br(freeze(icmp))
1744 // to br(icmp(freeze ...)).
1745 for (unsigned i = 0, e = PN->getNumIncomingValues(); i != e; ++i) {
1746 BasicBlock *PredBB = PN->getIncomingBlock(i);
1747 if (BranchInst *PredBr = dyn_cast<BranchInst>(PredBB->getTerminator()))
1748 if (PredBr->isUnconditional()) {
1749 PredBBs[0] = PredBB;
1750 // Try to duplicate BB into PredBB.
1751 if (duplicateCondBranchOnPHIIntoPred(BB, PredBBs))
1752 return true;
1753 }
1754 }
1755
1756 return false;
1757}
1758
1759/// processBranchOnXOR - We have an otherwise unthreadable conditional branch on
1760/// a xor instruction in the current block. See if there are any
1761/// simplifications we can do based on inputs to the xor.
1763 BasicBlock *BB = BO->getParent();
1764
1765 // If either the LHS or RHS of the xor is a constant, don't do this
1766 // optimization.
1767 if (isa<ConstantInt>(BO->getOperand(0)) ||
1768 isa<ConstantInt>(BO->getOperand(1)))
1769 return false;
1770
1771 // If the first instruction in BB isn't a phi, we won't be able to infer
1772 // anything special about any particular predecessor.
1773 if (!isa<PHINode>(BB->front()))
1774 return false;
1775
1776 // If this BB is a landing pad, we won't be able to split the edge into it.
1777 if (BB->isEHPad())
1778 return false;
1779
1780 // If we have a xor as the branch input to this block, and we know that the
1781 // LHS or RHS of the xor in any predecessor is true/false, then we can clone
1782 // the condition into the predecessor and fix that value to true, saving some
1783 // logical ops on that path and encouraging other paths to simplify.
1784 //
1785 // This copies something like this:
1786 //
1787 // BB:
1788 // %X = phi i1 [1], [%X']
1789 // %Y = icmp eq i32 %A, %B
1790 // %Z = xor i1 %X, %Y
1791 // br i1 %Z, ...
1792 //
1793 // Into:
1794 // BB':
1795 // %Y = icmp ne i32 %A, %B
1796 // br i1 %Y, ...
1797
1798 PredValueInfoTy XorOpValues;
1799 bool isLHS = true;
1800 if (!computeValueKnownInPredecessors(BO->getOperand(0), BB, XorOpValues,
1801 WantInteger, BO)) {
1802 assert(XorOpValues.empty());
1803 if (!computeValueKnownInPredecessors(BO->getOperand(1), BB, XorOpValues,
1804 WantInteger, BO))
1805 return false;
1806 isLHS = false;
1807 }
1808
1809 assert(!XorOpValues.empty() &&
1810 "computeValueKnownInPredecessors returned true with no values");
1811
1812 // Scan the information to see which is most popular: true or false. The
1813 // predecessors can be of the set true, false, or undef.
1814 unsigned NumTrue = 0, NumFalse = 0;
1815 for (const auto &XorOpValue : XorOpValues) {
1816 if (isa<UndefValue>(XorOpValue.first))
1817 // Ignore undefs for the count.
1818 continue;
1819 if (cast<ConstantInt>(XorOpValue.first)->isZero())
1820 ++NumFalse;
1821 else
1822 ++NumTrue;
1823 }
1824
1825 // Determine which value to split on, true, false, or undef if neither.
1826 ConstantInt *SplitVal = nullptr;
1827 if (NumTrue > NumFalse)
1828 SplitVal = ConstantInt::getTrue(BB->getContext());
1829 else if (NumTrue != 0 || NumFalse != 0)
1830 SplitVal = ConstantInt::getFalse(BB->getContext());
1831
1832 // Collect all of the blocks that this can be folded into so that we can
1833 // factor this once and clone it once.
1834 SmallVector<BasicBlock*, 8> BlocksToFoldInto;
1835 for (const auto &XorOpValue : XorOpValues) {
1836 if (XorOpValue.first != SplitVal && !isa<UndefValue>(XorOpValue.first))
1837 continue;
1838
1839 BlocksToFoldInto.push_back(XorOpValue.second);
1840 }
1841
1842 // If we inferred a value for all of the predecessors, then duplication won't
1843 // help us. However, we can just replace the LHS or RHS with the constant.
1844 if (BlocksToFoldInto.size() ==
1845 cast<PHINode>(BB->front()).getNumIncomingValues()) {
1846 if (!SplitVal) {
1847 // If all preds provide undef, just nuke the xor, because it is undef too.
1849 BO->eraseFromParent();
1850 } else if (SplitVal->isZero() && BO != BO->getOperand(isLHS)) {
1851 // If all preds provide 0, replace the xor with the other input.
1852 BO->replaceAllUsesWith(BO->getOperand(isLHS));
1853 BO->eraseFromParent();
1854 } else {
1855 // If all preds provide 1, set the computed value to 1.
1856 BO->setOperand(!isLHS, SplitVal);
1857 }
1858
1859 return true;
1860 }
1861
1862 // If any of predecessors end with an indirect goto, we can't change its
1863 // destination.
1864 if (any_of(BlocksToFoldInto, [](BasicBlock *Pred) {
1865 return isa<IndirectBrInst>(Pred->getTerminator());
1866 }))
1867 return false;
1868
1869 // Try to duplicate BB into PredBB.
1870 return duplicateCondBranchOnPHIIntoPred(BB, BlocksToFoldInto);
1871}
1872
1873/// addPHINodeEntriesForMappedBlock - We're adding 'NewPred' as a new
1874/// predecessor to the PHIBB block. If it has PHI nodes, add entries for
1875/// NewPred using the entries from OldPred (suitably mapped).
1877 BasicBlock *OldPred,
1878 BasicBlock *NewPred,
1880 for (PHINode &PN : PHIBB->phis()) {
1881 // Ok, we have a PHI node. Figure out what the incoming value was for the
1882 // DestBlock.
1883 Value *IV = PN.getIncomingValueForBlock(OldPred);
1884
1885 // Remap the value if necessary.
1886 if (Instruction *Inst = dyn_cast<Instruction>(IV)) {
1888 if (I != ValueMap.end())
1889 IV = I->second;
1890 }
1891
1892 PN.addIncoming(IV, NewPred);
1893 }
1894}
1895
1896/// Merge basic block BB into its sole predecessor if possible.
1898 BasicBlock *SinglePred = BB->getSinglePredecessor();
1899 if (!SinglePred)
1900 return false;
1901
1902 const Instruction *TI = SinglePred->getTerminator();
1903 if (TI->isSpecialTerminator() || TI->getNumSuccessors() != 1 ||
1904 SinglePred == BB || hasAddressTakenAndUsed(BB))
1905 return false;
1906
1907 // If SinglePred was a loop header, BB becomes one.
1908 if (LoopHeaders.erase(SinglePred))
1909 LoopHeaders.insert(BB);
1910
1911 LVI->eraseBlock(SinglePred);
1912 MergeBasicBlockIntoOnlyPred(BB, DTU.get());
1913
1914 // Now that BB is merged into SinglePred (i.e. SinglePred code followed by
1915 // BB code within one basic block `BB`), we need to invalidate the LVI
1916 // information associated with BB, because the LVI information need not be
1917 // true for all of BB after the merge. For example,
1918 // Before the merge, LVI info and code is as follows:
1919 // SinglePred: <LVI info1 for %p val>
1920 // %y = use of %p
1921 // call @exit() // need not transfer execution to successor.
1922 // assume(%p) // from this point on %p is true
1923 // br label %BB
1924 // BB: <LVI info2 for %p val, i.e. %p is true>
1925 // %x = use of %p
1926 // br label exit
1927 //
1928 // Note that this LVI info for blocks BB and SinglPred is correct for %p
1929 // (info2 and info1 respectively). After the merge and the deletion of the
1930 // LVI info1 for SinglePred. We have the following code:
1931 // BB: <LVI info2 for %p val>
1932 // %y = use of %p
1933 // call @exit()
1934 // assume(%p)
1935 // %x = use of %p <-- LVI info2 is correct from here onwards.
1936 // br label exit
1937 // LVI info2 for BB is incorrect at the beginning of BB.
1938
1939 // Invalidate LVI information for BB if the LVI is not provably true for
1940 // all of BB.
1942 LVI->eraseBlock(BB);
1943 return true;
1944}
1945
1946/// Update the SSA form. NewBB contains instructions that are copied from BB.
1947/// ValueMapping maps old values in BB to new ones in NewBB.
1949 BasicBlock *BB, BasicBlock *NewBB,
1950 DenseMap<Instruction *, Value *> &ValueMapping) {
1951 // If there were values defined in BB that are used outside the block, then we
1952 // now have to update all uses of the value to use either the original value,
1953 // the cloned value, or some PHI derived value. This can require arbitrary
1954 // PHI insertion, of which we are prepared to do, clean these up now.
1955 SSAUpdater SSAUpdate;
1956 SmallVector<Use *, 16> UsesToRename;
1959
1960 for (Instruction &I : *BB) {
1961 // Scan all uses of this instruction to see if it is used outside of its
1962 // block, and if so, record them in UsesToRename.
1963 for (Use &U : I.uses()) {
1964 Instruction *User = cast<Instruction>(U.getUser());
1965 if (PHINode *UserPN = dyn_cast<PHINode>(User)) {
1966 if (UserPN->getIncomingBlock(U) == BB)
1967 continue;
1968 } else if (User->getParent() == BB)
1969 continue;
1970
1971 UsesToRename.push_back(&U);
1972 }
1973
1974 // Find debug values outside of the block
1975 findDbgValues(DbgValues, &I, &DPValues);
1976 llvm::erase_if(DbgValues, [&](const DbgValueInst *DbgVal) {
1977 return DbgVal->getParent() == BB;
1978 });
1979 llvm::erase_if(DPValues, [&](const DPValue *DPVal) {
1980 return DPVal->getParent() == BB;
1981 });
1982
1983 // If there are no uses outside the block, we're done with this instruction.
1984 if (UsesToRename.empty() && DbgValues.empty() && DPValues.empty())
1985 continue;
1986 LLVM_DEBUG(dbgs() << "JT: Renaming non-local uses of: " << I << "\n");
1987
1988 // We found a use of I outside of BB. Rename all uses of I that are outside
1989 // its block to be uses of the appropriate PHI node etc. See ValuesInBlocks
1990 // with the two values we know.
1991 SSAUpdate.Initialize(I.getType(), I.getName());
1992 SSAUpdate.AddAvailableValue(BB, &I);
1993 SSAUpdate.AddAvailableValue(NewBB, ValueMapping[&I]);
1994
1995 while (!UsesToRename.empty())
1996 SSAUpdate.RewriteUse(*UsesToRename.pop_back_val());
1997 if (!DbgValues.empty() || !DPValues.empty()) {
1998 SSAUpdate.UpdateDebugValues(&I, DbgValues);
1999 SSAUpdate.UpdateDebugValues(&I, DPValues);
2000 DbgValues.clear();
2001 DPValues.clear();
2002 }
2003
2004 LLVM_DEBUG(dbgs() << "\n");
2005 }
2006}
2007
2008/// Clone instructions in range [BI, BE) to NewBB. For PHI nodes, we only clone
2009/// arguments that come from PredBB. Return the map from the variables in the
2010/// source basic block to the variables in the newly created basic block.
2014 BasicBlock *PredBB) {
2015 // We are going to have to map operands from the source basic block to the new
2016 // copy of the block 'NewBB'. If there are PHI nodes in the source basic
2017 // block, evaluate them to account for entry from PredBB.
2019
2020 // Retargets llvm.dbg.value to any renamed variables.
2021 auto RetargetDbgValueIfPossible = [&](Instruction *NewInst) -> bool {
2022 auto DbgInstruction = dyn_cast<DbgValueInst>(NewInst);
2023 if (!DbgInstruction)
2024 return false;
2025
2026 SmallSet<std::pair<Value *, Value *>, 16> OperandsToRemap;
2027 for (auto DbgOperand : DbgInstruction->location_ops()) {
2028 auto DbgOperandInstruction = dyn_cast<Instruction>(DbgOperand);
2029 if (!DbgOperandInstruction)
2030 continue;
2031
2032 auto I = ValueMapping.find(DbgOperandInstruction);
2033 if (I != ValueMapping.end()) {
2034 OperandsToRemap.insert(
2035 std::pair<Value *, Value *>(DbgOperand, I->second));
2036 }
2037 }
2038
2039 for (auto &[OldOp, MappedOp] : OperandsToRemap)
2040 DbgInstruction->replaceVariableLocationOp(OldOp, MappedOp);
2041 return true;
2042 };
2043
2044 // Duplicate implementation of the above dbg.value code, using DPValues
2045 // instead.
2046 auto RetargetDPValueIfPossible = [&](DPValue *DPV) {
2047 SmallSet<std::pair<Value *, Value *>, 16> OperandsToRemap;
2048 for (auto *Op : DPV->location_ops()) {
2049 Instruction *OpInst = dyn_cast<Instruction>(Op);
2050 if (!OpInst)
2051 continue;
2052
2053 auto I = ValueMapping.find(OpInst);
2054 if (I != ValueMapping.end())
2055 OperandsToRemap.insert({OpInst, I->second});
2056 }
2057
2058 for (auto &[OldOp, MappedOp] : OperandsToRemap)
2059 DPV->replaceVariableLocationOp(OldOp, MappedOp);
2060 };
2061
2062 BasicBlock *RangeBB = BI->getParent();
2063
2064 // Clone the phi nodes of the source basic block into NewBB. The resulting
2065 // phi nodes are trivial since NewBB only has one predecessor, but SSAUpdater
2066 // might need to rewrite the operand of the cloned phi.
2067 for (; PHINode *PN = dyn_cast<PHINode>(BI); ++BI) {
2068 PHINode *NewPN = PHINode::Create(PN->getType(), 1, PN->getName(), NewBB);
2069 NewPN->addIncoming(PN->getIncomingValueForBlock(PredBB), PredBB);
2070 ValueMapping[PN] = NewPN;
2071 }
2072
2073 // Clone noalias scope declarations in the threaded block. When threading a
2074 // loop exit, we would otherwise end up with two idential scope declarations
2075 // visible at the same time.
2076 SmallVector<MDNode *> NoAliasScopes;
2077 DenseMap<MDNode *, MDNode *> ClonedScopes;
2078 LLVMContext &Context = PredBB->getContext();
2079 identifyNoAliasScopesToClone(BI, BE, NoAliasScopes);
2080 cloneNoAliasScopes(NoAliasScopes, ClonedScopes, "thread", Context);
2081
2082 auto CloneAndRemapDbgInfo = [&](Instruction *NewInst, Instruction *From) {
2083 auto DPVRange = NewInst->cloneDebugInfoFrom(From);
2084 for (DPValue &DPV : filterDbgVars(DPVRange))
2085 RetargetDPValueIfPossible(&DPV);
2086 };
2087
2088 // Clone the non-phi instructions of the source basic block into NewBB,
2089 // keeping track of the mapping and using it to remap operands in the cloned
2090 // instructions.
2091 for (; BI != BE; ++BI) {
2092 Instruction *New = BI->clone();
2093 New->setName(BI->getName());
2094 New->insertInto(NewBB, NewBB->end());
2095 ValueMapping[&*BI] = New;
2096 adaptNoAliasScopes(New, ClonedScopes, Context);
2097
2098 CloneAndRemapDbgInfo(New, &*BI);
2099
2100 if (RetargetDbgValueIfPossible(New))
2101 continue;
2102
2103 // Remap operands to patch up intra-block references.
2104 for (unsigned i = 0, e = New->getNumOperands(); i != e; ++i)
2105 if (Instruction *Inst = dyn_cast<Instruction>(New->getOperand(i))) {
2107 if (I != ValueMapping.end())
2108 New->setOperand(i, I->second);
2109 }
2110 }
2111
2112 // There may be DPValues on the terminator, clone directly from marker
2113 // to marker as there isn't an instruction there.
2114 if (BE != RangeBB->end() && BE->hasDbgRecords()) {
2115 // Dump them at the end.
2116 DPMarker *Marker = RangeBB->getMarker(BE);
2117 DPMarker *EndMarker = NewBB->createMarker(NewBB->end());
2118 auto DPVRange = EndMarker->cloneDebugInfoFrom(Marker, std::nullopt);
2119 for (DPValue &DPV : filterDbgVars(DPVRange))
2120 RetargetDPValueIfPossible(&DPV);
2121 }
2122
2123 return ValueMapping;
2124}
2125
2126/// Attempt to thread through two successive basic blocks.
2128 Value *Cond) {
2129 // Consider:
2130 //
2131 // PredBB:
2132 // %var = phi i32* [ null, %bb1 ], [ @a, %bb2 ]
2133 // %tobool = icmp eq i32 %cond, 0
2134 // br i1 %tobool, label %BB, label ...
2135 //
2136 // BB:
2137 // %cmp = icmp eq i32* %var, null
2138 // br i1 %cmp, label ..., label ...
2139 //
2140 // We don't know the value of %var at BB even if we know which incoming edge
2141 // we take to BB. However, once we duplicate PredBB for each of its incoming
2142 // edges (say, PredBB1 and PredBB2), we know the value of %var in each copy of
2143 // PredBB. Then we can thread edges PredBB1->BB and PredBB2->BB through BB.
2144
2145 // Require that BB end with a Branch for simplicity.
2146 BranchInst *CondBr = dyn_cast<BranchInst>(BB->getTerminator());
2147 if (!CondBr)
2148 return false;
2149
2150 // BB must have exactly one predecessor.
2151 BasicBlock *PredBB = BB->getSinglePredecessor();
2152 if (!PredBB)
2153 return false;
2154
2155 // Require that PredBB end with a conditional Branch. If PredBB ends with an
2156 // unconditional branch, we should be merging PredBB and BB instead. For
2157 // simplicity, we don't deal with a switch.
2158 BranchInst *PredBBBranch = dyn_cast<BranchInst>(PredBB->getTerminator());
2159 if (!PredBBBranch || PredBBBranch->isUnconditional())
2160 return false;
2161
2162 // If PredBB has exactly one incoming edge, we don't gain anything by copying
2163 // PredBB.
2164 if (PredBB->getSinglePredecessor())
2165 return false;
2166
2167 // Don't thread through PredBB if it contains a successor edge to itself, in
2168 // which case we would infinite loop. Suppose we are threading an edge from
2169 // PredPredBB through PredBB and BB to SuccBB with PredBB containing a
2170 // successor edge to itself. If we allowed jump threading in this case, we
2171 // could duplicate PredBB and BB as, say, PredBB.thread and BB.thread. Since
2172 // PredBB.thread has a successor edge to PredBB, we would immediately come up
2173 // with another jump threading opportunity from PredBB.thread through PredBB
2174 // and BB to SuccBB. This jump threading would repeatedly occur. That is, we
2175 // would keep peeling one iteration from PredBB.
2176 if (llvm::is_contained(successors(PredBB), PredBB))
2177 return false;
2178
2179 // Don't thread across a loop header.
2180 if (LoopHeaders.count(PredBB))
2181 return false;
2182
2183 // Avoid complication with duplicating EH pads.
2184 if (PredBB->isEHPad())
2185 return false;
2186
2187 // Find a predecessor that we can thread. For simplicity, we only consider a
2188 // successor edge out of BB to which we thread exactly one incoming edge into
2189 // PredBB.
2190 unsigned ZeroCount = 0;
2191 unsigned OneCount = 0;
2192 BasicBlock *ZeroPred = nullptr;
2193 BasicBlock *OnePred = nullptr;
2194 for (BasicBlock *P : predecessors(PredBB)) {
2195 // If PredPred ends with IndirectBrInst, we can't handle it.
2196 if (isa<IndirectBrInst>(P->getTerminator()))
2197 continue;
2198 if (ConstantInt *CI = dyn_cast_or_null<ConstantInt>(
2200 if (CI->isZero()) {
2201 ZeroCount++;
2202 ZeroPred = P;
2203 } else if (CI->isOne()) {
2204 OneCount++;
2205 OnePred = P;
2206 }
2207 }
2208 }
2209
2210 // Disregard complicated cases where we have to thread multiple edges.
2211 BasicBlock *PredPredBB;
2212 if (ZeroCount == 1) {
2213 PredPredBB = ZeroPred;
2214 } else if (OneCount == 1) {
2215 PredPredBB = OnePred;
2216 } else {
2217 return false;
2218 }
2219
2220 BasicBlock *SuccBB = CondBr->getSuccessor(PredPredBB == ZeroPred);
2221
2222 // If threading to the same block as we come from, we would infinite loop.
2223 if (SuccBB == BB) {
2224 LLVM_DEBUG(dbgs() << " Not threading across BB '" << BB->getName()
2225 << "' - would thread to self!\n");
2226 return false;
2227 }
2228
2229 // If threading this would thread across a loop header, don't thread the edge.
2230 // See the comments above findLoopHeaders for justifications and caveats.
2231 if (LoopHeaders.count(BB) || LoopHeaders.count(SuccBB)) {
2232 LLVM_DEBUG({
2233 bool BBIsHeader = LoopHeaders.count(BB);
2234 bool SuccIsHeader = LoopHeaders.count(SuccBB);
2235 dbgs() << " Not threading across "
2236 << (BBIsHeader ? "loop header BB '" : "block BB '")
2237 << BB->getName() << "' to dest "
2238 << (SuccIsHeader ? "loop header BB '" : "block BB '")
2239 << SuccBB->getName()
2240 << "' - it might create an irreducible loop!\n";
2241 });
2242 return false;
2243 }
2244
2245 // Compute the cost of duplicating BB and PredBB.
2246 unsigned BBCost = getJumpThreadDuplicationCost(
2247 TTI, BB, BB->getTerminator(), BBDupThreshold);
2248 unsigned PredBBCost = getJumpThreadDuplicationCost(
2249 TTI, PredBB, PredBB->getTerminator(), BBDupThreshold);
2250
2251 // Give up if costs are too high. We need to check BBCost and PredBBCost
2252 // individually before checking their sum because getJumpThreadDuplicationCost
2253 // return (unsigned)~0 for those basic blocks that cannot be duplicated.
2254 if (BBCost > BBDupThreshold || PredBBCost > BBDupThreshold ||
2255 BBCost + PredBBCost > BBDupThreshold) {
2256 LLVM_DEBUG(dbgs() << " Not threading BB '" << BB->getName()
2257 << "' - Cost is too high: " << PredBBCost
2258 << " for PredBB, " << BBCost << "for BB\n");
2259 return false;
2260 }
2261
2262 // Now we are ready to duplicate PredBB.
2263 threadThroughTwoBasicBlocks(PredPredBB, PredBB, BB, SuccBB);
2264 return true;
2265}
2266
2268 BasicBlock *PredBB,
2269 BasicBlock *BB,
2270 BasicBlock *SuccBB) {
2271 LLVM_DEBUG(dbgs() << " Threading through '" << PredBB->getName() << "' and '"
2272 << BB->getName() << "'\n");
2273
2274 // Build BPI/BFI before any changes are made to IR.
2275 bool HasProfile = doesBlockHaveProfileData(BB);
2276 auto *BFI = getOrCreateBFI(HasProfile);
2277 auto *BPI = getOrCreateBPI(BFI != nullptr);
2278
2279 BranchInst *CondBr = cast<BranchInst>(BB->getTerminator());
2280 BranchInst *PredBBBranch = cast<BranchInst>(PredBB->getTerminator());
2281
2282 BasicBlock *NewBB =
2283 BasicBlock::Create(PredBB->getContext(), PredBB->getName() + ".thread",
2284 PredBB->getParent(), PredBB);
2285 NewBB->moveAfter(PredBB);
2286
2287 // Set the block frequency of NewBB.
2288 if (BFI) {
2289 assert(BPI && "It's expected BPI to exist along with BFI");
2290 auto NewBBFreq = BFI->getBlockFreq(PredPredBB) *
2291 BPI->getEdgeProbability(PredPredBB, PredBB);
2292 BFI->setBlockFreq(NewBB, NewBBFreq);
2293 }
2294
2295 // We are going to have to map operands from the original BB block to the new
2296 // copy of the block 'NewBB'. If there are PHI nodes in PredBB, evaluate them
2297 // to account for entry from PredPredBB.
2299 cloneInstructions(PredBB->begin(), PredBB->end(), NewBB, PredPredBB);
2300
2301 // Copy the edge probabilities from PredBB to NewBB.
2302 if (BPI)
2303 BPI->copyEdgeProbabilities(PredBB, NewBB);
2304
2305 // Update the terminator of PredPredBB to jump to NewBB instead of PredBB.
2306 // This eliminates predecessors from PredPredBB, which requires us to simplify
2307 // any PHI nodes in PredBB.
2308 Instruction *PredPredTerm = PredPredBB->getTerminator();
2309 for (unsigned i = 0, e = PredPredTerm->getNumSuccessors(); i != e; ++i)
2310 if (PredPredTerm->getSuccessor(i) == PredBB) {
2311 PredBB->removePredecessor(PredPredBB, true);
2312 PredPredTerm->setSuccessor(i, NewBB);
2313 }
2314
2315 addPHINodeEntriesForMappedBlock(PredBBBranch->getSuccessor(0), PredBB, NewBB,
2316 ValueMapping);
2317 addPHINodeEntriesForMappedBlock(PredBBBranch->getSuccessor(1), PredBB, NewBB,
2318 ValueMapping);
2319
2320 DTU->applyUpdatesPermissive(
2321 {{DominatorTree::Insert, NewBB, CondBr->getSuccessor(0)},
2322 {DominatorTree::Insert, NewBB, CondBr->getSuccessor(1)},
2323 {DominatorTree::Insert, PredPredBB, NewBB},
2324 {DominatorTree::Delete, PredPredBB, PredBB}});
2325
2326 updateSSA(PredBB, NewBB, ValueMapping);
2327
2328 // Clean up things like PHI nodes with single operands, dead instructions,
2329 // etc.
2330 SimplifyInstructionsInBlock(NewBB, TLI);
2331 SimplifyInstructionsInBlock(PredBB, TLI);
2332
2333 SmallVector<BasicBlock *, 1> PredsToFactor;
2334 PredsToFactor.push_back(NewBB);
2335 threadEdge(BB, PredsToFactor, SuccBB);
2336}
2337
2338/// tryThreadEdge - Thread an edge if it's safe and profitable to do so.
2340 BasicBlock *BB, const SmallVectorImpl<BasicBlock *> &PredBBs,
2341 BasicBlock *SuccBB) {
2342 // If threading to the same block as we come from, we would infinite loop.
2343 if (SuccBB == BB) {
2344 LLVM_DEBUG(dbgs() << " Not threading across BB '" << BB->getName()
2345 << "' - would thread to self!\n");
2346 return false;
2347 }
2348
2349 // If threading this would thread across a loop header, don't thread the edge.
2350 // See the comments above findLoopHeaders for justifications and caveats.
2351 if (LoopHeaders.count(BB) || LoopHeaders.count(SuccBB)) {
2352 LLVM_DEBUG({
2353 bool BBIsHeader = LoopHeaders.count(BB);
2354 bool SuccIsHeader = LoopHeaders.count(SuccBB);
2355 dbgs() << " Not threading across "
2356 << (BBIsHeader ? "loop header BB '" : "block BB '") << BB->getName()
2357 << "' to dest " << (SuccIsHeader ? "loop header BB '" : "block BB '")
2358 << SuccBB->getName() << "' - it might create an irreducible loop!\n";
2359 });
2360 return false;
2361 }
2362
2363 unsigned JumpThreadCost = getJumpThreadDuplicationCost(
2364 TTI, BB, BB->getTerminator(), BBDupThreshold);
2365 if (JumpThreadCost > BBDupThreshold) {
2366 LLVM_DEBUG(dbgs() << " Not threading BB '" << BB->getName()
2367 << "' - Cost is too high: " << JumpThreadCost << "\n");
2368 return false;
2369 }
2370
2371 threadEdge(BB, PredBBs, SuccBB);
2372 return true;
2373}
2374
2375/// threadEdge - We have decided that it is safe and profitable to factor the
2376/// blocks in PredBBs to one predecessor, then thread an edge from it to SuccBB
2377/// across BB. Transform the IR to reflect this change.
2379 const SmallVectorImpl<BasicBlock *> &PredBBs,
2380 BasicBlock *SuccBB) {
2381 assert(SuccBB != BB && "Don't create an infinite loop");
2382
2383 assert(!LoopHeaders.count(BB) && !LoopHeaders.count(SuccBB) &&
2384 "Don't thread across loop headers");
2385
2386 // Build BPI/BFI before any changes are made to IR.
2387 bool HasProfile = doesBlockHaveProfileData(BB);
2388 auto *BFI = getOrCreateBFI(HasProfile);
2389 auto *BPI = getOrCreateBPI(BFI != nullptr);
2390
2391 // And finally, do it! Start by factoring the predecessors if needed.
2392 BasicBlock *PredBB;
2393 if (PredBBs.size() == 1)
2394 PredBB = PredBBs[0];
2395 else {
2396 LLVM_DEBUG(dbgs() << " Factoring out " << PredBBs.size()
2397 << " common predecessors.\n");
2398 PredBB = splitBlockPreds(BB, PredBBs, ".thr_comm");
2399 }
2400
2401 // And finally, do it!
2402 LLVM_DEBUG(dbgs() << " Threading edge from '" << PredBB->getName()
2403 << "' to '" << SuccBB->getName()
2404 << ", across block:\n " << *BB << "\n");
2405
2406 LVI->threadEdge(PredBB, BB, SuccBB);
2407
2409 BB->getName()+".thread",
2410 BB->getParent(), BB);
2411 NewBB->moveAfter(PredBB);
2412
2413 // Set the block frequency of NewBB.
2414 if (BFI) {
2415 assert(BPI && "It's expected BPI to exist along with BFI");
2416 auto NewBBFreq =
2417 BFI->getBlockFreq(PredBB) * BPI->getEdgeProbability(PredBB, BB);
2418 BFI->setBlockFreq(NewBB, NewBBFreq);
2419 }
2420
2421 // Copy all the instructions from BB to NewBB except the terminator.
2423 cloneInstructions(BB->begin(), std::prev(BB->end()), NewBB, PredBB);
2424
2425 // We didn't copy the terminator from BB over to NewBB, because there is now
2426 // an unconditional jump to SuccBB. Insert the unconditional jump.
2427 BranchInst *NewBI = BranchInst::Create(SuccBB, NewBB);
2428 NewBI->setDebugLoc(BB->getTerminator()->getDebugLoc());
2429
2430 // Check to see if SuccBB has PHI nodes. If so, we need to add entries to the
2431 // PHI nodes for NewBB now.
2432 addPHINodeEntriesForMappedBlock(SuccBB, BB, NewBB, ValueMapping);
2433
2434 // Update the terminator of PredBB to jump to NewBB instead of BB. This
2435 // eliminates predecessors from BB, which requires us to simplify any PHI
2436 // nodes in BB.
2437 Instruction *PredTerm = PredBB->getTerminator();
2438 for (unsigned i = 0, e = PredTerm->getNumSuccessors(); i != e; ++i)
2439 if (PredTerm->getSuccessor(i) == BB) {
2440 BB->removePredecessor(PredBB, true);
2441 PredTerm->setSuccessor(i, NewBB);
2442 }
2443
2444 // Enqueue required DT updates.
2445 DTU->applyUpdatesPermissive({{DominatorTree::Insert, NewBB, SuccBB},
2446 {DominatorTree::Insert, PredBB, NewBB},
2447 {DominatorTree::Delete, PredBB, BB}});
2448
2449 updateSSA(BB, NewBB, ValueMapping);
2450
2451 // At this point, the IR is fully up to date and consistent. Do a quick scan
2452 // over the new instructions and zap any that are constants or dead. This
2453 // frequently happens because of phi translation.
2454 SimplifyInstructionsInBlock(NewBB, TLI);
2455
2456 // Update the edge weight from BB to SuccBB, which should be less than before.
2457 updateBlockFreqAndEdgeWeight(PredBB, BB, NewBB, SuccBB, BFI, BPI, HasProfile);
2458
2459 // Threaded an edge!
2460 ++NumThreads;
2461}
2462
2463/// Create a new basic block that will be the predecessor of BB and successor of
2464/// all blocks in Preds. When profile data is available, update the frequency of
2465/// this new block.
2466BasicBlock *JumpThreadingPass::splitBlockPreds(BasicBlock *BB,
2468 const char *Suffix) {
2470
2471 // Collect the frequencies of all predecessors of BB, which will be used to
2472 // update the edge weight of the result of splitting predecessors.
2474 auto *BFI = getBFI();
2475 if (BFI) {
2476 auto *BPI = getOrCreateBPI(true);
2477 for (auto *Pred : Preds)
2478 FreqMap.insert(std::make_pair(
2479 Pred, BFI->getBlockFreq(Pred) * BPI->getEdgeProbability(Pred, BB)));
2480 }
2481
2482 // In the case when BB is a LandingPad block we create 2 new predecessors
2483 // instead of just one.
2484 if (BB->isLandingPad()) {
2485 std::string NewName = std::string(Suffix) + ".split-lp";
2486 SplitLandingPadPredecessors(BB, Preds, Suffix, NewName.c_str(), NewBBs);
2487 } else {
2488 NewBBs.push_back(SplitBlockPredecessors(BB, Preds, Suffix));
2489 }
2490
2491 std::vector<DominatorTree::UpdateType> Updates;
2492 Updates.reserve((2 * Preds.size()) + NewBBs.size());
2493 for (auto *NewBB : NewBBs) {
2494 BlockFrequency NewBBFreq(0);
2495 Updates.push_back({DominatorTree::Insert, NewBB, BB});
2496 for (auto *Pred : predecessors(NewBB)) {
2497 Updates.push_back({DominatorTree::Delete, Pred, BB});
2498 Updates.push_back({DominatorTree::Insert, Pred, NewBB});
2499 if (BFI) // Update frequencies between Pred -> NewBB.
2500 NewBBFreq += FreqMap.lookup(Pred);
2501 }
2502 if (BFI) // Apply the summed frequency to NewBB.
2503 BFI->setBlockFreq(NewBB, NewBBFreq);
2504 }
2505
2506 DTU->applyUpdatesPermissive(Updates);
2507 return NewBBs[0];
2508}
2509
2510bool JumpThreadingPass::doesBlockHaveProfileData(BasicBlock *BB) {
2511 const Instruction *TI = BB->getTerminator();
2512 if (!TI || TI->getNumSuccessors() < 2)
2513 return false;
2514
2515 return hasValidBranchWeightMD(*TI);
2516}
2517
2518/// Update the block frequency of BB and branch weight and the metadata on the
2519/// edge BB->SuccBB. This is done by scaling the weight of BB->SuccBB by 1 -
2520/// Freq(PredBB->BB) / Freq(BB->SuccBB).
2521void JumpThreadingPass::updateBlockFreqAndEdgeWeight(BasicBlock *PredBB,
2522 BasicBlock *BB,
2523 BasicBlock *NewBB,
2524 BasicBlock *SuccBB,
2525 BlockFrequencyInfo *BFI,
2527 bool HasProfile) {
2528 assert(((BFI && BPI) || (!BFI && !BFI)) &&
2529 "Both BFI & BPI should either be set or unset");
2530
2531 if (!BFI) {
2532 assert(!HasProfile &&
2533 "It's expected to have BFI/BPI when profile info exists");
2534 return;
2535 }
2536
2537 // As the edge from PredBB to BB is deleted, we have to update the block
2538 // frequency of BB.
2539 auto BBOrigFreq = BFI->getBlockFreq(BB);
2540 auto NewBBFreq = BFI->getBlockFreq(NewBB);
2541 auto BB2SuccBBFreq = BBOrigFreq * BPI->getEdgeProbability(BB, SuccBB);
2542 auto BBNewFreq = BBOrigFreq - NewBBFreq;
2543 BFI->setBlockFreq(BB, BBNewFreq);
2544
2545 // Collect updated outgoing edges' frequencies from BB and use them to update
2546 // edge probabilities.
2547 SmallVector<uint64_t, 4> BBSuccFreq;
2548 for (BasicBlock *Succ : successors(BB)) {
2549 auto SuccFreq = (Succ == SuccBB)
2550 ? BB2SuccBBFreq - NewBBFreq
2551 : BBOrigFreq * BPI->getEdgeProbability(BB, Succ);
2552 BBSuccFreq.push_back(SuccFreq.getFrequency());
2553 }
2554
2555 uint64_t MaxBBSuccFreq = *llvm::max_element(BBSuccFreq);
2556
2558 if (MaxBBSuccFreq == 0)
2559 BBSuccProbs.assign(BBSuccFreq.size(),
2560 {1, static_cast<unsigned>(BBSuccFreq.size())});
2561 else {
2562 for (uint64_t Freq : BBSuccFreq)
2563 BBSuccProbs.push_back(
2564 BranchProbability::getBranchProbability(Freq, MaxBBSuccFreq));
2565 // Normalize edge probabilities so that they sum up to one.
2567 BBSuccProbs.end());
2568 }
2569
2570 // Update edge probabilities in BPI.
2571 BPI->setEdgeProbability(BB, BBSuccProbs);
2572
2573 // Update the profile metadata as well.
2574 //
2575 // Don't do this if the profile of the transformed blocks was statically
2576 // estimated. (This could occur despite the function having an entry
2577 // frequency in completely cold parts of the CFG.)
2578 //
2579 // In this case we don't want to suggest to subsequent passes that the
2580 // calculated weights are fully consistent. Consider this graph:
2581 //
2582 // check_1
2583 // 50% / |
2584 // eq_1 | 50%
2585 // \ |
2586 // check_2
2587 // 50% / |
2588 // eq_2 | 50%
2589 // \ |
2590 // check_3
2591 // 50% / |
2592 // eq_3 | 50%
2593 // \ |
2594 //
2595 // Assuming the blocks check_* all compare the same value against 1, 2 and 3,
2596 // the overall probabilities are inconsistent; the total probability that the
2597 // value is either 1, 2 or 3 is 150%.
2598 //
2599 // As a consequence if we thread eq_1 -> check_2 to check_3, check_2->check_3
2600 // becomes 0%. This is even worse if the edge whose probability becomes 0% is
2601 // the loop exit edge. Then based solely on static estimation we would assume
2602 // the loop was extremely hot.
2603 //
2604 // FIXME this locally as well so that BPI and BFI are consistent as well. We
2605 // shouldn't make edges extremely likely or unlikely based solely on static
2606 // estimation.
2607 if (BBSuccProbs.size() >= 2 && HasProfile) {
2609 for (auto Prob : BBSuccProbs)
2610 Weights.push_back(Prob.getNumerator());
2611
2612 auto TI = BB->getTerminator();
2613 setBranchWeights(*TI, Weights);
2614 }
2615}
2616
2617/// duplicateCondBranchOnPHIIntoPred - PredBB contains an unconditional branch
2618/// to BB which contains an i1 PHI node and a conditional branch on that PHI.
2619/// If we can duplicate the contents of BB up into PredBB do so now, this
2620/// improves the odds that the branch will be on an analyzable instruction like
2621/// a compare.
2623 BasicBlock *BB, const SmallVectorImpl<BasicBlock *> &PredBBs) {
2624 assert(!PredBBs.empty() && "Can't handle an empty set");
2625
2626 // If BB is a loop header, then duplicating this block outside the loop would
2627 // cause us to transform this into an irreducible loop, don't do this.
2628 // See the comments above findLoopHeaders for justifications and caveats.
2629 if (LoopHeaders.count(BB)) {
2630 LLVM_DEBUG(dbgs() << " Not duplicating loop header '" << BB->getName()
2631 << "' into predecessor block '" << PredBBs[0]->getName()
2632 << "' - it might create an irreducible loop!\n");
2633 return false;
2634 }
2635
2636 unsigned DuplicationCost = getJumpThreadDuplicationCost(
2637 TTI, BB, BB->getTerminator(), BBDupThreshold);
2638 if (DuplicationCost > BBDupThreshold) {
2639 LLVM_DEBUG(dbgs() << " Not duplicating BB '" << BB->getName()
2640 << "' - Cost is too high: " << DuplicationCost << "\n");
2641 return false;
2642 }
2643
2644 // And finally, do it! Start by factoring the predecessors if needed.
2645 std::vector<DominatorTree::UpdateType> Updates;
2646 BasicBlock *PredBB;
2647 if (PredBBs.size() == 1)
2648 PredBB = PredBBs[0];
2649 else {
2650 LLVM_DEBUG(dbgs() << " Factoring out " << PredBBs.size()
2651 << " common predecessors.\n");
2652 PredBB = splitBlockPreds(BB, PredBBs, ".thr_comm");
2653 }
2654 Updates.push_back({DominatorTree::Delete, PredBB, BB});
2655
2656 // Okay, we decided to do this! Clone all the instructions in BB onto the end
2657 // of PredBB.
2658 LLVM_DEBUG(dbgs() << " Duplicating block '" << BB->getName()
2659 << "' into end of '" << PredBB->getName()
2660 << "' to eliminate branch on phi. Cost: "
2661 << DuplicationCost << " block is:" << *BB << "\n");
2662
2663 // Unless PredBB ends with an unconditional branch, split the edge so that we
2664 // can just clone the bits from BB into the end of the new PredBB.
2665 BranchInst *OldPredBranch = dyn_cast<BranchInst>(PredBB->getTerminator());
2666
2667 if (!OldPredBranch || !OldPredBranch->isUnconditional()) {
2668 BasicBlock *OldPredBB = PredBB;
2669 PredBB = SplitEdge(OldPredBB, BB);
2670 Updates.push_back({DominatorTree::Insert, OldPredBB, PredBB});
2671 Updates.push_back({DominatorTree::Insert, PredBB, BB});
2672 Updates.push_back({DominatorTree::Delete, OldPredBB, BB});
2673 OldPredBranch = cast<BranchInst>(PredBB->getTerminator());
2674 }
2675
2676 // We are going to have to map operands from the original BB block into the
2677 // PredBB block. Evaluate PHI nodes in BB.
2678 DenseMap<Instruction*, Value*> ValueMapping;
2679
2680 BasicBlock::iterator BI = BB->begin();
2681 for (; PHINode *PN = dyn_cast<PHINode>(BI); ++BI)
2682 ValueMapping[PN] = PN->getIncomingValueForBlock(PredBB);
2683 // Clone the non-phi instructions of BB into PredBB, keeping track of the
2684 // mapping and using it to remap operands in the cloned instructions.
2685 for (; BI != BB->end(); ++BI) {
2686 Instruction *New = BI->clone();
2687 New->insertInto(PredBB, OldPredBranch->getIterator());
2688
2689 // Remap operands to patch up intra-block references.
2690 for (unsigned i = 0, e = New->getNumOperands(); i != e; ++i)
2691 if (Instruction *Inst = dyn_cast<Instruction>(New->getOperand(i))) {
2692 DenseMap<Instruction*, Value*>::iterator I = ValueMapping.find(Inst);
2693 if (I != ValueMapping.end())
2694 New->setOperand(i, I->second);
2695 }
2696
2697 // If this instruction can be simplified after the operands are updated,
2698 // just use the simplified value instead. This frequently happens due to
2699 // phi translation.
2701 New,
2702 {BB->getModule()->getDataLayout(), TLI, nullptr, nullptr, New})) {
2703 ValueMapping[&*BI] = IV;
2704 if (!New->mayHaveSideEffects()) {
2705 New->eraseFromParent();
2706 New = nullptr;
2707 // Clone debug-info on the elided instruction to the destination
2708 // position.
2709 OldPredBranch->cloneDebugInfoFrom(&*BI, std::nullopt, true);
2710 }
2711 } else {
2712 ValueMapping[&*BI] = New;
2713 }
2714 if (New) {
2715 // Otherwise, insert the new instruction into the block.
2716 New->setName(BI->getName());
2717 // Clone across any debug-info attached to the old instruction.
2718 New->cloneDebugInfoFrom(&*BI);
2719 // Update Dominance from simplified New instruction operands.
2720 for (unsigned i = 0, e = New->getNumOperands(); i != e; ++i)
2721 if (BasicBlock *SuccBB = dyn_cast<BasicBlock>(New->getOperand(i)))
2722 Updates.push_back({DominatorTree::Insert, PredBB, SuccBB});
2723 }
2724 }
2725
2726 // Check to see if the targets of the branch had PHI nodes. If so, we need to
2727 // add entries to the PHI nodes for branch from PredBB now.
2728 BranchInst *BBBranch = cast<BranchInst>(BB->getTerminator());
2729 addPHINodeEntriesForMappedBlock(BBBranch->getSuccessor(0), BB, PredBB,
2730 ValueMapping);
2731 addPHINodeEntriesForMappedBlock(BBBranch->getSuccessor(1), BB, PredBB,
2732 ValueMapping);
2733
2734 updateSSA(BB, PredBB, ValueMapping);
2735
2736 // PredBB no longer jumps to BB, remove entries in the PHI node for the edge
2737 // that we nuked.
2738 BB->removePredecessor(PredBB, true);
2739
2740 // Remove the unconditional branch at the end of the PredBB block.
2741 OldPredBranch->eraseFromParent();
2742 if (auto *BPI = getBPI())
2743 BPI->copyEdgeProbabilities(BB, PredBB);
2744 DTU->applyUpdatesPermissive(Updates);
2745
2746 ++NumDupes;
2747 return true;
2748}
2749
2750// Pred is a predecessor of BB with an unconditional branch to BB. SI is
2751// a Select instruction in Pred. BB has other predecessors and SI is used in
2752// a PHI node in BB. SI has no other use.
2753// A new basic block, NewBB, is created and SI is converted to compare and
2754// conditional branch. SI is erased from parent.
2756 SelectInst *SI, PHINode *SIUse,
2757 unsigned Idx) {
2758 // Expand the select.
2759 //
2760 // Pred --
2761 // | v
2762 // | NewBB
2763 // | |
2764 // |-----
2765 // v
2766 // BB
2767 BranchInst *PredTerm = cast<BranchInst>(Pred->getTerminator());
2768 BasicBlock *NewBB = BasicBlock::Create(BB->getContext(), "select.unfold",
2769 BB->getParent(), BB);
2770 // Move the unconditional branch to NewBB.
2771 PredTerm->removeFromParent();
2772 PredTerm->insertInto(NewBB, NewBB->end());
2773 // Create a conditional branch and update PHI nodes.
2774 auto *BI = BranchInst::Create(NewBB, BB, SI->getCondition(), Pred);
2775 BI->applyMergedLocation(PredTerm->getDebugLoc(), SI->getDebugLoc());
2776 BI->copyMetadata(*SI, {LLVMContext::MD_prof});
2777 SIUse->setIncomingValue(Idx, SI->getFalseValue());
2778 SIUse->addIncoming(SI->getTrueValue(), NewBB);
2779
2780 uint64_t TrueWeight = 1;
2781 uint64_t FalseWeight = 1;
2782 // Copy probabilities from 'SI' to created conditional branch in 'Pred'.
2783 if (extractBranchWeights(*SI, TrueWeight, FalseWeight) &&
2784 (TrueWeight + FalseWeight) != 0) {
2787 TrueWeight, TrueWeight + FalseWeight));
2789 FalseWeight, TrueWeight + FalseWeight));
2790 // Update BPI if exists.
2791 if (auto *BPI = getBPI())
2792 BPI->setEdgeProbability(Pred, BP);
2793 }
2794 // Set the block frequency of NewBB.
2795 if (auto *BFI = getBFI()) {
2796 if ((TrueWeight + FalseWeight) == 0) {
2797 TrueWeight = 1;
2798 FalseWeight = 1;
2799 }
2801 TrueWeight, TrueWeight + FalseWeight);
2802 auto NewBBFreq = BFI->getBlockFreq(Pred) * PredToNewBBProb;
2803 BFI->setBlockFreq(NewBB, NewBBFreq);
2804 }
2805
2806 // The select is now dead.
2807 SI->eraseFromParent();
2808 DTU->applyUpdatesPermissive({{DominatorTree::Insert, NewBB, BB},
2809 {DominatorTree::Insert, Pred, NewBB}});
2810
2811 // Update any other PHI nodes in BB.
2812 for (BasicBlock::iterator BI = BB->begin();
2813 PHINode *Phi = dyn_cast<PHINode>(BI); ++BI)
2814 if (Phi != SIUse)
2815 Phi->addIncoming(Phi->getIncomingValueForBlock(Pred), NewBB);
2816}
2817
2819 PHINode *CondPHI = dyn_cast<PHINode>(SI->getCondition());
2820
2821 if (!CondPHI || CondPHI->getParent() != BB)
2822 return false;
2823
2824 for (unsigned I = 0, E = CondPHI->getNumIncomingValues(); I != E; ++I) {
2825 BasicBlock *Pred = CondPHI->getIncomingBlock(I);
2826 SelectInst *PredSI = dyn_cast<SelectInst>(CondPHI->getIncomingValue(I));
2827
2828 // The second and third condition can be potentially relaxed. Currently
2829 // the conditions help to simplify the code and allow us to reuse existing
2830 // code, developed for tryToUnfoldSelect(CmpInst *, BasicBlock *)
2831 if (!PredSI || PredSI->getParent() != Pred || !PredSI->hasOneUse())
2832 continue;
2833
2834 BranchInst *PredTerm = dyn_cast<BranchInst>(Pred->getTerminator());
2835 if (!PredTerm || !PredTerm->isUnconditional())
2836 continue;
2837
2838 unfoldSelectInstr(Pred, BB, PredSI, CondPHI, I);
2839 return true;
2840 }
2841 return false;
2842}
2843
2844/// tryToUnfoldSelect - Look for blocks of the form
2845/// bb1:
2846/// %a = select
2847/// br bb2
2848///
2849/// bb2:
2850/// %p = phi [%a, %bb1] ...
2851/// %c = icmp %p
2852/// br i1 %c
2853///
2854/// And expand the select into a branch structure if one of its arms allows %c
2855/// to be folded. This later enables threading from bb1 over bb2.
2857 BranchInst *CondBr = dyn_cast<BranchInst>(BB->getTerminator());
2858 PHINode *CondLHS = dyn_cast<PHINode>(CondCmp->getOperand(0));
2859 Constant *CondRHS = cast<Constant>(CondCmp->getOperand(1));
2860
2861 if (!CondBr || !CondBr->isConditional() || !CondLHS ||
2862 CondLHS->getParent() != BB)
2863 return false;
2864
2865 for (unsigned I = 0, E = CondLHS->getNumIncomingValues(); I != E; ++I) {
2866 BasicBlock *Pred = CondLHS->getIncomingBlock(I);
2867 SelectInst *SI = dyn_cast<SelectInst>(CondLHS->getIncomingValue(I));
2868
2869 // Look if one of the incoming values is a select in the corresponding
2870 // predecessor.
2871 if (!SI || SI->getParent() != Pred || !SI->hasOneUse())
2872 continue;
2873
2874 BranchInst *PredTerm = dyn_cast<BranchInst>(Pred->getTerminator());
2875 if (!PredTerm || !PredTerm->isUnconditional())
2876 continue;
2877
2878 // Now check if one of the select values would allow us to constant fold the
2879 // terminator in BB. We don't do the transform if both sides fold, those
2880 // cases will be threaded in any case.
2881 LazyValueInfo::Tristate LHSFolds =
2882 LVI->getPredicateOnEdge(CondCmp->getPredicate(), SI->getOperand(1),
2883 CondRHS, Pred, BB, CondCmp);
2884 LazyValueInfo::Tristate RHSFolds =
2885 LVI->getPredicateOnEdge(CondCmp->getPredicate(), SI->getOperand(2),
2886 CondRHS, Pred, BB, CondCmp);
2887 if ((LHSFolds != LazyValueInfo::Unknown ||
2888 RHSFolds != LazyValueInfo::Unknown) &&
2889 LHSFolds != RHSFolds) {
2890 unfoldSelectInstr(Pred, BB, SI, CondLHS, I);
2891 return true;
2892 }
2893 }
2894 return false;
2895}
2896
2897/// tryToUnfoldSelectInCurrBB - Look for PHI/Select or PHI/CMP/Select in the
2898/// same BB in the form
2899/// bb:
2900/// %p = phi [false, %bb1], [true, %bb2], [false, %bb3], [true, %bb4], ...
2901/// %s = select %p, trueval, falseval
2902///
2903/// or
2904///
2905/// bb:
2906/// %p = phi [0, %bb1], [1, %bb2], [0, %bb3], [1, %bb4], ...
2907/// %c = cmp %p, 0
2908/// %s = select %c, trueval, falseval
2909///
2910/// And expand the select into a branch structure. This later enables
2911/// jump-threading over bb in this pass.
2912///
2913/// Using the similar approach of SimplifyCFG::FoldCondBranchOnPHI(), unfold
2914/// select if the associated PHI has at least one constant. If the unfolded
2915/// select is not jump-threaded, it will be folded again in the later
2916/// optimizations.
2918 // This transform would reduce the quality of msan diagnostics.
2919 // Disable this transform under MemorySanitizer.
2920 if (BB->getParent()->hasFnAttribute(Attribute::SanitizeMemory))
2921 return false;
2922
2923 // If threading this would thread across a loop header, don't thread the edge.
2924 // See the comments above findLoopHeaders for justifications and caveats.
2925 if (LoopHeaders.count(BB))
2926 return false;
2927
2928 for (BasicBlock::iterator BI = BB->begin();
2929 PHINode *PN = dyn_cast<PHINode>(BI); ++BI) {
2930 // Look for a Phi having at least one constant incoming value.
2931 if (llvm::all_of(PN->incoming_values(),
2932 [](Value *V) { return !isa<ConstantInt>(V); }))
2933 continue;
2934
2935 auto isUnfoldCandidate = [BB](SelectInst *SI, Value *V) {
2936 using namespace PatternMatch;
2937
2938 // Check if SI is in BB and use V as condition.
2939 if (SI->getParent() != BB)
2940 return false;
2941 Value *Cond = SI->getCondition();
2942 bool IsAndOr = match(SI, m_CombineOr(m_LogicalAnd(), m_LogicalOr()));
2943 return Cond && Cond == V && Cond->getType()->isIntegerTy(1) && !IsAndOr;
2944 };
2945
2946 SelectInst *SI = nullptr;
2947 for (Use &U : PN->uses()) {
2948 if (ICmpInst *Cmp = dyn_cast<ICmpInst>(U.getUser())) {
2949 // Look for a ICmp in BB that compares PN with a constant and is the
2950 // condition of a Select.
2951 if (Cmp->getParent() == BB && Cmp->hasOneUse() &&
2952 isa<ConstantInt>(Cmp->getOperand(1 - U.getOperandNo())))
2953 if (SelectInst *SelectI = dyn_cast<SelectInst>(Cmp->user_back()))
2954 if (isUnfoldCandidate(SelectI, Cmp->use_begin()->get())) {
2955 SI = SelectI;
2956 break;
2957 }
2958 } else if (SelectInst *SelectI = dyn_cast<SelectInst>(U.getUser())) {
2959 // Look for a Select in BB that uses PN as condition.
2960 if (isUnfoldCandidate(SelectI, U.get())) {
2961 SI = SelectI;
2962 break;
2963 }
2964 }
2965 }
2966
2967 if (!SI)
2968 continue;
2969 // Expand the select.
2970 Value *Cond = SI->getCondition();
2971 if (!isGuaranteedNotToBeUndefOrPoison(Cond, nullptr, SI))
2972 Cond = new FreezeInst(Cond, "cond.fr", SI->getIterator());
2973 MDNode *BranchWeights = getBranchWeightMDNode(*SI);
2974 Instruction *Term =
2975 SplitBlockAndInsertIfThen(Cond, SI, false, BranchWeights);
2976 BasicBlock *SplitBB = SI->getParent();
2977 BasicBlock *NewBB = Term->getParent();
2978 PHINode *NewPN = PHINode::Create(SI->getType(), 2, "", SI->getIterator());
2979 NewPN->addIncoming(SI->getTrueValue(), Term->getParent());
2980 NewPN->addIncoming(SI->getFalseValue(), BB);
2981 SI->replaceAllUsesWith(NewPN);
2982 SI->eraseFromParent();
2983 // NewBB and SplitBB are newly created blocks which require insertion.
2984 std::vector<DominatorTree::UpdateType> Updates;
2985 Updates.reserve((2 * SplitBB->getTerminator()->getNumSuccessors()) + 3);
2986 Updates.push_back({DominatorTree::Insert, BB, SplitBB});
2987 Updates.push_back({DominatorTree::Insert, BB, NewBB});
2988 Updates.push_back({DominatorTree::Insert, NewBB, SplitBB});
2989 // BB's successors were moved to SplitBB, update DTU accordingly.
2990 for (auto *Succ : successors(SplitBB)) {
2991 Updates.push_back({DominatorTree::Delete, BB, Succ});
2992 Updates.push_back({DominatorTree::Insert, SplitBB, Succ});
2993 }
2994 DTU->applyUpdatesPermissive(Updates);
2995 return true;
2996 }
2997 return false;
2998}
2999
3000/// Try to propagate a guard from the current BB into one of its predecessors
3001/// in case if another branch of execution implies that the condition of this
3002/// guard is always true. Currently we only process the simplest case that
3003/// looks like:
3004///
3005/// Start:
3006/// %cond = ...
3007/// br i1 %cond, label %T1, label %F1
3008/// T1:
3009/// br label %Merge
3010/// F1:
3011/// br label %Merge
3012/// Merge:
3013/// %condGuard = ...
3014/// call void(i1, ...) @llvm.experimental.guard( i1 %condGuard )[ "deopt"() ]
3015///
3016/// And cond either implies condGuard or !condGuard. In this case all the
3017/// instructions before the guard can be duplicated in both branches, and the
3018/// guard is then threaded to one of them.
3020 using namespace PatternMatch;
3021
3022 // We only want to deal with two predecessors.
3023 BasicBlock *Pred1, *Pred2;
3024 auto PI = pred_begin(BB), PE = pred_end(BB);
3025 if (PI == PE)
3026 return false;
3027 Pred1 = *PI++;
3028 if (PI == PE)
3029 return false;
3030 Pred2 = *PI++;
3031 if (PI != PE)
3032 return false;
3033 if (Pred1 == Pred2)
3034 return false;
3035
3036 // Try to thread one of the guards of the block.
3037 // TODO: Look up deeper than to immediate predecessor?
3038 auto *Parent = Pred1->getSinglePredecessor();
3039 if (!Parent || Parent != Pred2->getSinglePredecessor())
3040 return false;
3041
3042 if (auto *BI = dyn_cast<BranchInst>(Parent->getTerminator()))
3043 for (auto &I : *BB)
3044 if (isGuard(&I) && threadGuard(BB, cast<IntrinsicInst>(&I), BI))
3045 return true;
3046
3047 return false;
3048}
3049
3050/// Try to propagate the guard from BB which is the lower block of a diamond
3051/// to one of its branches, in case if diamond's condition implies guard's
3052/// condition.
3054 BranchInst *BI) {
3055 assert(BI->getNumSuccessors() == 2 && "Wrong number of successors?");
3056 assert(BI->isConditional() && "Unconditional branch has 2 successors?");
3057 Value *GuardCond = Guard->getArgOperand(0);
3058 Value *BranchCond = BI->getCondition();
3059 BasicBlock *TrueDest = BI->getSuccessor(0);
3060 BasicBlock *FalseDest = BI->getSuccessor(1);
3061
3062 auto &DL = BB->getModule()->getDataLayout();
3063 bool TrueDestIsSafe = false;
3064 bool FalseDestIsSafe = false;
3065
3066 // True dest is safe if BranchCond => GuardCond.
3067 auto Impl = isImpliedCondition(BranchCond, GuardCond, DL);
3068 if (Impl && *Impl)
3069 TrueDestIsSafe = true;
3070 else {
3071 // False dest is safe if !BranchCond => GuardCond.
3072 Impl = isImpliedCondition(BranchCond, GuardCond, DL, /* LHSIsTrue */ false);
3073 if (Impl && *Impl)
3074 FalseDestIsSafe = true;
3075 }
3076
3077 if (!TrueDestIsSafe && !FalseDestIsSafe)
3078 return false;
3079
3080 BasicBlock *PredUnguardedBlock = TrueDestIsSafe ? TrueDest : FalseDest;
3081 BasicBlock *PredGuardedBlock = FalseDestIsSafe ? TrueDest : FalseDest;
3082
3083 ValueToValueMapTy UnguardedMapping, GuardedMapping;
3084 Instruction *AfterGuard = Guard->getNextNode();
3085 unsigned Cost =
3086 getJumpThreadDuplicationCost(TTI, BB, AfterGuard, BBDupThreshold);
3087 if (Cost > BBDupThreshold)
3088 return false;
3089 // Duplicate all instructions before the guard and the guard itself to the
3090 // branch where implication is not proved.
3092 BB, PredGuardedBlock, AfterGuard, GuardedMapping, *DTU);
3093 assert(GuardedBlock && "Could not create the guarded block?");
3094 // Duplicate all instructions before the guard in the unguarded branch.
3095 // Since we have successfully duplicated the guarded block and this block
3096 // has fewer instructions, we expect it to succeed.
3098 BB, PredUnguardedBlock, Guard, UnguardedMapping, *DTU);
3099 assert(UnguardedBlock && "Could not create the unguarded block?");
3100 LLVM_DEBUG(dbgs() << "Moved guard " << *Guard << " to block "
3101 << GuardedBlock->getName() << "\n");
3102 // Some instructions before the guard may still have uses. For them, we need
3103 // to create Phi nodes merging their copies in both guarded and unguarded
3104 // branches. Those instructions that have no uses can be just removed.
3106 for (auto BI = BB->begin(); &*BI != AfterGuard; ++BI)
3107 if (!isa<PHINode>(&*BI))
3108 ToRemove.push_back(&*BI);
3109
3110 BasicBlock::iterator InsertionPoint = BB->getFirstInsertionPt();
3111 assert(InsertionPoint != BB->end() && "Empty block?");
3112 // Substitute with Phis & remove.
3113 for (auto *Inst : reverse(ToRemove)) {
3114 if (!Inst->use_empty()) {
3115 PHINode *NewPN = PHINode::Create(Inst->getType(), 2);
3116 NewPN->addIncoming(UnguardedMapping[Inst], UnguardedBlock);
3117 NewPN->addIncoming(GuardedMapping[Inst], GuardedBlock);
3118 NewPN->insertBefore(InsertionPoint);
3119 Inst->replaceAllUsesWith(NewPN);
3120 }
3121 Inst->dropDbgRecords();
3122 Inst->eraseFromParent();
3123 }
3124 return true;
3125}
3126
3127PreservedAnalyses JumpThreadingPass::getPreservedAnalysis() const {
3131
3132 // TODO: We would like to preserve BPI/BFI. Enable once all paths update them.
3133 // TODO: Would be nice to verify BPI/BFI consistency as well.
3134 return PA;
3135}
3136
3137template <typename AnalysisT>
3138typename AnalysisT::Result *JumpThreadingPass::runExternalAnalysis() {
3139 assert(FAM && "Can't run external analysis without FunctionAnalysisManager");
3140
3141 // If there were no changes since last call to 'runExternalAnalysis' then all
3142 // analysis is either up to date or explicitly invalidated. Just go ahead and
3143 // run the "external" analysis.
3144 if (!ChangedSinceLastAnalysisUpdate) {
3145 assert(!DTU->hasPendingUpdates() &&
3146 "Lost update of 'ChangedSinceLastAnalysisUpdate'?");
3147 // Run the "external" analysis.
3148 return &FAM->getResult<AnalysisT>(*F);
3149 }
3150 ChangedSinceLastAnalysisUpdate = false;
3151
3152 auto PA = getPreservedAnalysis();
3153 // TODO: This shouldn't be needed once 'getPreservedAnalysis' reports BPI/BFI
3154 // as preserved.
3155 PA.preserve<BranchProbabilityAnalysis>();
3156 PA.preserve<BlockFrequencyAnalysis>();
3157 // Report everything except explicitly preserved as invalid.
3158 FAM->invalidate(*F, PA);
3159 // Update DT/PDT.
3160 DTU->flush();
3161 // Make sure DT/PDT are valid before running "external" analysis.
3162 assert(DTU->getDomTree().verify(DominatorTree::VerificationLevel::Fast));
3163 assert((!DTU->hasPostDomTree() ||
3164 DTU->getPostDomTree().verify(
3166 // Run the "external" analysis.
3167 auto *Result = &FAM->getResult<AnalysisT>(*F);
3168 // Update analysis JumpThreading depends on and not explicitly preserved.
3169 TTI = &FAM->getResult<TargetIRAnalysis>(*F);
3170 TLI = &FAM->getResult<TargetLibraryAnalysis>(*F);
3171 AA = &FAM->getResult<AAManager>(*F);
3172
3173 return Result;
3174}
3175
3176BranchProbabilityInfo *JumpThreadingPass::getBPI() {
3177 if (!BPI) {
3178 assert(FAM && "Can't create BPI without FunctionAnalysisManager");
3180 }
3181 return *BPI;
3182}
3183
3184BlockFrequencyInfo *JumpThreadingPass::getBFI() {
3185 if (!BFI) {
3186 assert(FAM && "Can't create BFI without FunctionAnalysisManager");
3188 }
3189 return *BFI;
3190}
3191
3192// Important note on validity of BPI/BFI. JumpThreading tries to preserve
3193// BPI/BFI as it goes. Thus if cached instance exists it will be updated.
3194// Otherwise, new instance of BPI/BFI is created (up to date by definition).
3195BranchProbabilityInfo *JumpThreadingPass::getOrCreateBPI(bool Force) {
3196 auto *Res = getBPI();
3197 if (Res)
3198 return Res;
3199
3200 if (Force)
3201 BPI = runExternalAnalysis<BranchProbabilityAnalysis>();
3202
3203 return *BPI;
3204}
3205
3206BlockFrequencyInfo *JumpThreadingPass::getOrCreateBFI(bool Force) {
3207 auto *Res = getBFI();
3208 if (Res)
3209 return Res;
3210
3211 if (Force)
3212 BFI = runExternalAnalysis<BlockFrequencyAnalysis>();
3213
3214 return *BFI;
3215}
MachineBasicBlock MachineBasicBlock::iterator DebugLoc DL
Rewrite undef for PHI
ReachingDefAnalysis InstSet & ToRemove
static const Function * getParent(const Value *V)
BlockVerifier::State From
static GCRegistry::Add< CoreCLRGC > E("coreclr", "CoreCLR-compatible GC")
This file contains the declarations for the subclasses of Constant, which represent the different fla...
Returns the sub type a function will return at a given Idx Should correspond to the result type of an ExtractValue instruction executed with just that one unsigned Idx
#define LLVM_DEBUG(X)
Definition: Debug.h:101
This file defines the DenseMap class.
This file defines the DenseSet and SmallDenseSet classes.
uint64_t Size
This is the interface for a simple mod/ref and alias analysis over globals.
This file provides various utilities for inspecting and working with the control flow graph in LLVM I...
static unsigned getBestDestForJumpOnUndef(BasicBlock *BB)
GetBestDestForBranchOnUndef - If we determine that the specified block ends in an undefined jump,...
static cl::opt< unsigned > PhiDuplicateThreshold("jump-threading-phi-threshold", cl::desc("Max PHIs in BB to duplicate for jump threading"), cl::init(76), cl::Hidden)
static bool replaceFoldableUses(Instruction *Cond, Value *ToVal, BasicBlock *KnownAtEndOfBB)
static cl::opt< unsigned > BBDuplicateThreshold("jump-threading-threshold", cl::desc("Max block size to duplicate for jump threading"), cl::init(6), cl::Hidden)
static cl::opt< bool > ThreadAcrossLoopHeaders("jump-threading-across-loop-headers", cl::desc("Allow JumpThreading to thread across loop headers, for testing"), cl::init(false), cl::Hidden)
static unsigned getJumpThreadDuplicationCost(const TargetTransformInfo *TTI, BasicBlock *BB, Instruction *StopAt, unsigned Threshold)
Return the cost of duplicating a piece of this block from first non-phi and before StopAt instruction...
static BasicBlock * findMostPopularDest(BasicBlock *BB, const SmallVectorImpl< std::pair< BasicBlock *, BasicBlock * > > &PredToDestList)
findMostPopularDest - The specified list contains multiple possible threadable destinations.
static Constant * getKnownConstant(Value *Val, ConstantPreference Preference)
getKnownConstant - Helper method to determine if we can thread over a terminator with the given value...
static cl::opt< unsigned > ImplicationSearchThreshold("jump-threading-implication-search-threshold", cl::desc("The number of predecessors to search for a stronger " "condition to use to thread over a weaker condition"), cl::init(3), cl::Hidden)
static void addPHINodeEntriesForMappedBlock(BasicBlock *PHIBB, BasicBlock *OldPred, BasicBlock *NewPred, DenseMap< Instruction *, Value * > &ValueMap)
addPHINodeEntriesForMappedBlock - We're adding 'NewPred' as a new predecessor to the PHIBB block.
static bool isOpDefinedInBlock(Value *Op, BasicBlock *BB)
Return true if Op is an instruction defined in the given block.
static void updatePredecessorProfileMetadata(PHINode *PN, BasicBlock *BB)
static bool hasAddressTakenAndUsed(BasicBlock *BB)
See the comments on JumpThreadingPass.
static bool isZero(Value *V, const DataLayout &DL, DominatorTree *DT, AssumptionCache *AC)
Definition: Lint.cpp:531
#define F(x, y, z)
Definition: MD5.cpp:55
#define I(x, y, z)
Definition: MD5.cpp:58
This file implements a map that provides insertion order iteration.
This file provides utility analysis objects describing memory locations.
This file contains the declarations for metadata subclasses.
Module.h This file contains the declarations for the Module class.
LLVMContext & Context
#define P(N)
ppc ctr loops verify
This header defines various interfaces for pass management in LLVM.
This file contains the declarations for profiling metadata utility functions.
const SmallVectorImpl< MachineOperand > & Cond
assert(ImpDefSCC.getReg()==AMDGPU::SCC &&ImpDefSCC.isDef())
This file contains some templates that are useful if you are working with the STL at all.
This file defines the SmallPtrSet class.
This file defines the SmallVector class.
This file defines the 'Statistic' class, which is designed to be an easy way to expose various metric...
#define STATISTIC(VARNAME, DESC)
Definition: Statistic.h:167
This pass exposes codegen information to IR-level passes.
This defines the Use class.
Value * RHS
Value * LHS
static const uint32_t IV[8]
Definition: blake3_impl.h:78
A manager for alias analyses.
A container for analyses that lazily runs them and caches their results.
Definition: PassManager.h:348
void invalidate(IRUnitT &IR, const PreservedAnalyses &PA)
Invalidate cached analyses for an IR unit.
PassT::Result * getCachedResult(IRUnitT &IR) const
Get the cached result of an analysis pass for a given IR unit.
Definition: PassManager.h:519
PassT::Result & getResult(IRUnitT &IR, ExtraArgTs... ExtraArgs)
Get the result of an analysis pass for a given IR unit.
Definition: PassManager.h:500
ArrayRef - Represent a constant reference to an array (0 or more elements consecutively in memory),...
Definition: ArrayRef.h:41
LLVM Basic Block Representation.
Definition: BasicBlock.h:60
iterator end()
Definition: BasicBlock.h:442
DPMarker * getMarker(InstListType::iterator It)
Return the DPMarker for the position given by It, so that DbgRecords can be inserted there.
iterator begin()
Instruction iterator methods.
Definition: BasicBlock.h:429
iterator_range< const_phi_iterator > phis() const
Returns a range that iterates over the phis in the basic block.
Definition: BasicBlock.h:498
const_iterator getFirstInsertionPt() const
Returns an iterator to the first instruction in this block that is suitable for inserting a non-PHI i...
Definition: BasicBlock.cpp:396
bool hasAddressTaken() const
Returns true if there are any uses of this basic block other than direct branches,...
Definition: BasicBlock.h:639
InstListType::const_iterator const_iterator
Definition: BasicBlock.h:165
const Instruction & front() const
Definition: BasicBlock.h:452
static BasicBlock * Create(LLVMContext &Context, const Twine &Name="", Function *Parent=nullptr, BasicBlock *InsertBefore=nullptr)
Creates a new BasicBlock.
Definition: BasicBlock.h:198
void moveAfter(BasicBlock *MovePos)
Unlink this basic block from its current function and insert it right after MovePos in the function M...
Definition: BasicBlock.cpp:271
bool hasNPredecessors(unsigned N) const
Return true if this block has exactly N predecessors.
Definition: BasicBlock.cpp:461
const BasicBlock * getSinglePredecessor() const
Return the predecessor of this block if it has a single predecessor block.
Definition: BasicBlock.cpp:439
DPMarker * createMarker(Instruction *I)
Attach a DPMarker to the given instruction.
Definition: BasicBlock.cpp:44
const Function * getParent() const
Return the enclosing method, or null if none.
Definition: BasicBlock.h:205
InstListType::iterator iterator
Instruction iterators...
Definition: BasicBlock.h:164
LLVMContext & getContext() const
Get the context in which this basic block lives.
Definition: BasicBlock.cpp:155
bool isLandingPad() const
Return true if this basic block is a landing pad.
Definition: BasicBlock.cpp:659
bool isEHPad() const
Return true if this basic block is an exception handling block.
Definition: BasicBlock.h:656
const Instruction * getTerminator() const LLVM_READONLY
Returns the terminator instruction if the block is well formed or null if the block is not well forme...
Definition: BasicBlock.h:220
const Module * getModule() const
Return the module owning the function this basic block belongs to, or nullptr if the function does no...
Definition: BasicBlock.cpp:276
void removePredecessor(BasicBlock *Pred, bool KeepOneInputPHIs=false)
Update PHI nodes in this BasicBlock before removal of predecessor Pred.
Definition: BasicBlock.cpp:496
This class is a wrapper over an AAResults, and it is intended to be used only when there are no IR ch...
void disableDominatorTree()
Disable the use of the dominator tree during alias analysis queries.
The address of a basic block.
Definition: Constants.h:888
static BlockAddress * get(Function *F, BasicBlock *BB)
Return a BlockAddress for the specified function and basic block.
Definition: Constants.cpp:1846
Analysis pass which computes BlockFrequencyInfo.
BlockFrequencyInfo pass uses BlockFrequencyInfoImpl implementation to estimate IR basic block frequen...
Conditional or Unconditional Branch instruction.
static BranchInst * Create(BasicBlock *IfTrue, BasicBlock::iterator InsertBefore)
bool isConditional() const
unsigned getNumSuccessors() const
BasicBlock * getSuccessor(unsigned i) const
bool isUnconditional() const
Value * getCondition() const
Analysis pass which computes BranchProbabilityInfo.
Analysis providing branch probability information.
void setEdgeProbability(const BasicBlock *Src, const SmallVectorImpl< BranchProbability > &Probs)
Set the raw probabilities for all edges from the given block.
BranchProbability getEdgeProbability(const BasicBlock *Src, unsigned IndexInSuccessors) const
Get an edge's probability, relative to other out-edges of the Src.
void copyEdgeProbabilities(BasicBlock *Src, BasicBlock *Dst)
Copy outgoing edge probabilities from Src to Dst.
static BranchProbability getBranchProbability(uint64_t Numerator, uint64_t Denominator)
uint32_t getNumerator() const
BranchProbability getCompl() const
static void normalizeProbabilities(ProbabilityIter Begin, ProbabilityIter End)
Value * getArgOperand(unsigned i) const
Definition: InstrTypes.h:1648
This class represents a function call, abstracting a target machine's calling convention.
This is the base class for all instructions that perform data casts.
Definition: InstrTypes.h:579
static CastInst * CreateBitOrPointerCast(Value *S, Type *Ty, const Twine &Name, BasicBlock::iterator InsertBefore)
Create a BitCast, a PtrToInt, or an IntToPTr cast instruction.
This class is the base class for the comparison instructions.
Definition: InstrTypes.h:955
Predicate
This enumeration lists the possible predicates for CmpInst subclasses.
Definition: InstrTypes.h:965
Predicate getPredicate() const
Return the predicate for this instruction.
Definition: InstrTypes.h:1066
static Constant * getNot(Constant *C)
Definition: Constants.cpp:2531
static Constant * getCompare(unsigned short pred, Constant *C1, Constant *C2, bool OnlyIfReduced=false)
Return an ICmp or FCmp comparison operator constant expression.
Definition: Constants.cpp:2328
This is the shared class of boolean and integer constants.
Definition: Constants.h:79
bool isOne() const
This is just a convenience method to make client code smaller for a common case.
Definition: Constants.h:210
static ConstantInt * getTrue(LLVMContext &Context)
Definition: Constants.cpp:849
bool isZero() const
This is just a convenience method to make client code smaller for a common code.
Definition: Constants.h:204
static ConstantInt * getFalse(LLVMContext &Context)
Definition: Constants.cpp:856
const APInt & getValue() const
Return the constant as an APInt value reference.
Definition: Constants.h:144
static ConstantInt * getBool(LLVMContext &Context, bool V)
Definition: Constants.cpp:863
This class represents a range of values.
Definition: ConstantRange.h:47
ConstantRange add(const ConstantRange &Other) const
Return a new range representing the possible values resulting from an addition of a value in this ran...
static ConstantRange makeExactICmpRegion(CmpInst::Predicate Pred, const APInt &Other)
Produce the exact range such that all values in the returned range satisfy the given predicate with a...
ConstantRange inverse() const
Return a new range that is the logical not of the current set.
bool contains(const APInt &Val) const
Return true if the specified value is in the set.
This is an important base class in LLVM.
Definition: Constant.h:41
void removeDeadConstantUsers() const
If there are any dead constant users dangling off of this constant, remove them.
Definition: Constants.cpp:722
Per-instruction record of debug-info.
iterator_range< simple_ilist< DbgRecord >::iterator > cloneDebugInfoFrom(DPMarker *From, std::optional< simple_ilist< DbgRecord >::iterator > FromHere, bool InsertAtHead=false)
Clone all DPMarkers from From into this marker.
Record of a variable value-assignment, aka a non instruction representation of the dbg....
This class represents an Operation in the Expression.
A parsed version of the target data layout string in and methods for querying it.
Definition: DataLayout.h:110
const BasicBlock * getParent() const
This represents the llvm.dbg.value instruction.
ValueT lookup(const_arg_type_t< KeyT > Val) const
lookup - Return the entry for the specified key, or a default constructed value if no such entry exis...
Definition: DenseMap.h:202
iterator find(const_arg_type_t< KeyT > Val)
Definition: DenseMap.h:155
iterator end()
Definition: DenseMap.h:84
std::pair< iterator, bool > insert(const std::pair< KeyT, ValueT > &KV)
Definition: DenseMap.h:220
Implements a dense probed hash-table based set.
Definition: DenseSet.h:271
void flush()
Apply all pending updates to available trees and flush all BasicBlocks awaiting deletion.
Analysis pass which computes a DominatorTree.
Definition: Dominators.h:279
Concrete subclass of DominatorTreeBase that is used to compute a normal dominator tree.
Definition: Dominators.h:162
bool isReachableFromEntry(const Use &U) const
Provide an overload for a Use.
Definition: Dominators.cpp:321
This class represents a freeze function that returns random concrete value if an operand is either a ...
const BasicBlock & getEntryBlock() const
Definition: Function.h:782
bool hasFnAttribute(Attribute::AttrKind Kind) const
Return true if the function has the attribute.
Definition: Function.cpp:669
Module * getParent()
Get the module that this global value is contained inside of...
Definition: GlobalValue.h:655
This instruction compares its operands according to the predicate given to the constructor.
Indirect Branch Instruction.
void removeFromParent()
This method unlinks 'this' from the containing basic block, but does not delete it.
Definition: Instruction.cpp:88
iterator_range< simple_ilist< DbgRecord >::iterator > cloneDebugInfoFrom(const Instruction *From, std::optional< simple_ilist< DbgRecord >::iterator > FromHere=std::nullopt, bool InsertAtHead=false)
Clone any debug-info attached to From onto this instruction.
unsigned getNumSuccessors() const LLVM_READONLY
Return the number of successors that this instruction has.
void insertBefore(Instruction *InsertPos)
Insert an unlinked instruction into a basic block immediately before the specified instruction.
const DebugLoc & getDebugLoc() const
Return the debug location for this node as a DebugLoc.
Definition: Instruction.h:453
const Module * getModule() const
Return the module owning the function this instruction belongs to or nullptr it the function does not...
Definition: Instruction.cpp:80
void setAAMetadata(const AAMDNodes &N)
Sets the AA metadata on this instruction from the AAMDNodes structure.
Definition: Metadata.cpp:1718
bool isAtomic() const LLVM_READONLY
Return true if this instruction has an AtomicOrdering of unordered or higher.
const BasicBlock * getParent() const
Definition: Instruction.h:151
InstListType::iterator eraseFromParent()
This method unlinks 'this' from the containing basic block and deletes it.
BasicBlock * getSuccessor(unsigned Idx) const LLVM_READONLY
Return the specified successor. This instruction must be a terminator.
AAMDNodes getAAMetadata() const
Returns the AA metadata for this instruction.
Definition: Metadata.cpp:1704
unsigned getOpcode() const
Returns a member of one of the enums like Instruction::Add.
Definition: Instruction.h:251
void setDebugLoc(DebugLoc Loc)
Set the debug location information for this instruction.
Definition: Instruction.h:450
void setSuccessor(unsigned Idx, BasicBlock *BB)
Update the specified successor to point at the provided block.
bool isSpecialTerminator() const
Definition: Instruction.h:261
InstListType::iterator insertInto(BasicBlock *ParentBB, InstListType::iterator It)
Inserts an unlinked instruction into ParentBB at position It and returns the iterator of the inserted...
A wrapper class for inspecting calls to intrinsic functions.
Definition: IntrinsicInst.h:47
bool simplifyPartiallyRedundantLoad(LoadInst *LI)
simplifyPartiallyRedundantLoad - If LoadI is an obviously partially redundant load instruction,...
bool processBranchOnXOR(BinaryOperator *BO)
processBranchOnXOR - We have an otherwise unthreadable conditional branch on a xor instruction in the...
bool processGuards(BasicBlock *BB)
Try to propagate a guard from the current BB into one of its predecessors in case if another branch o...
DenseMap< Instruction *, Value * > cloneInstructions(BasicBlock::iterator BI, BasicBlock::iterator BE, BasicBlock *NewBB, BasicBlock *PredBB)
Clone instructions in range [BI, BE) to NewBB.
bool computeValueKnownInPredecessors(Value *V, BasicBlock *BB, jumpthreading::PredValueInfo &Result, jumpthreading::ConstantPreference Preference, Instruction *CxtI=nullptr)
void findLoopHeaders(Function &F)
findLoopHeaders - We do not want jump threading to turn proper loop structures into irreducible loops...
bool maybeMergeBasicBlockIntoOnlyPred(BasicBlock *BB)
Merge basic block BB into its sole predecessor if possible.
PreservedAnalyses run(Function &F, FunctionAnalysisManager &AM)
bool runImpl(Function &F, FunctionAnalysisManager *FAM, TargetLibraryInfo *TLI, TargetTransformInfo *TTI, LazyValueInfo *LVI, AAResults *AA, std::unique_ptr< DomTreeUpdater > DTU, std::optional< BlockFrequencyInfo * > BFI, std::optional< BranchProbabilityInfo * > BPI)
bool processBranchOnPHI(PHINode *PN)
processBranchOnPHI - We have an otherwise unthreadable conditional branch on a PHI node (or freeze PH...
bool maybethreadThroughTwoBasicBlocks(BasicBlock *BB, Value *Cond)
Attempt to thread through two successive basic blocks.
void unfoldSelectInstr(BasicBlock *Pred, BasicBlock *BB, SelectInst *SI, PHINode *SIUse, unsigned Idx)
DomTreeUpdater * getDomTreeUpdater() const
Constant * evaluateOnPredecessorEdge(BasicBlock *BB, BasicBlock *PredPredBB, Value *cond)
bool processThreadableEdges(Value *Cond, BasicBlock *BB, jumpthreading::ConstantPreference Preference, Instruction *CxtI=nullptr)
bool computeValueKnownInPredecessorsImpl(Value *V, BasicBlock *BB, jumpthreading::PredValueInfo &Result, jumpthreading::ConstantPreference Preference, DenseSet< Value * > &RecursionSet, Instruction *CxtI=nullptr)
computeValueKnownInPredecessors - Given a basic block BB and a value V, see if we can infer that the ...
bool processBlock(BasicBlock *BB)
processBlock - If there are any predecessors whose control can be threaded through to a successor,...
bool processImpliedCondition(BasicBlock *BB)
bool duplicateCondBranchOnPHIIntoPred(BasicBlock *BB, const SmallVectorImpl< BasicBlock * > &PredBBs)
duplicateCondBranchOnPHIIntoPred - PredBB contains an unconditional branch to BB which contains an i1...
void updateSSA(BasicBlock *BB, BasicBlock *NewBB, DenseMap< Instruction *, Value * > &ValueMapping)
Update the SSA form.
void threadThroughTwoBasicBlocks(BasicBlock *PredPredBB, BasicBlock *PredBB, BasicBlock *BB, BasicBlock *SuccBB)
bool tryThreadEdge(BasicBlock *BB, const SmallVectorImpl< BasicBlock * > &PredBBs, BasicBlock *SuccBB)
tryThreadEdge - Thread an edge if it's safe and profitable to do so.
bool tryToUnfoldSelect(CmpInst *CondCmp, BasicBlock *BB)
tryToUnfoldSelect - Look for blocks of the form bb1: a = select br bb2
bool tryToUnfoldSelectInCurrBB(BasicBlock *BB)
tryToUnfoldSelectInCurrBB - Look for PHI/Select or PHI/CMP/Select in the same BB in the form bb: p = ...
void threadEdge(BasicBlock *BB, const SmallVectorImpl< BasicBlock * > &PredBBs, BasicBlock *SuccBB)
threadEdge - We have decided that it is safe and profitable to factor the blocks in PredBBs to one pr...
bool threadGuard(BasicBlock *BB, IntrinsicInst *Guard, BranchInst *BI)
Try to propagate the guard from BB which is the lower block of a diamond to one of its branches,...
This is an important class for using LLVM in a threaded context.
Definition: LLVMContext.h:67
Analysis to compute lazy value information.
This pass computes, caches, and vends lazy value constraint information.
Definition: LazyValueInfo.h:31
void eraseBlock(BasicBlock *BB)
Inform the analysis cache that we have erased a block.
void threadEdge(BasicBlock *PredBB, BasicBlock *OldSucc, BasicBlock *NewSucc)
Inform the analysis cache that we have threaded an edge from PredBB to OldSucc to be from PredBB to N...
Tristate
This is used to return true/false/dunno results.
Definition: LazyValueInfo.h:61
Constant * getConstantOnEdge(Value *V, BasicBlock *FromBB, BasicBlock *ToBB, Instruction *CxtI=nullptr)
Determine whether the specified value is known to be a constant on the specified edge.
ConstantRange getConstantRangeOnEdge(Value *V, BasicBlock *FromBB, BasicBlock *ToBB, Instruction *CxtI=nullptr)
Return the ConstantRage constraint that is known to hold for the specified value on the specified edg...
Tristate getPredicateOnEdge(unsigned Pred, Value *V, Constant *C, BasicBlock *FromBB, BasicBlock *ToBB, Instruction *CxtI=nullptr)
Determine whether the specified value comparison with a constant is known to be true or false on the ...
Tristate getPredicateAt(unsigned Pred, Value *V, Constant *C, Instruction *CxtI, bool UseBlockValue)
Determine whether the specified value comparison with a constant is known to be true or false at the ...
Constant * getConstant(Value *V, Instruction *CxtI)
Determine whether the specified value is known to be a constant at the specified instruction.
void forgetValue(Value *V)
Remove information related to this value from the cache.
An instruction for reading from memory.
Definition: Instructions.h:184
AtomicOrdering getOrdering() const
Returns the ordering constraint of this load instruction.
Definition: Instructions.h:245
bool isUnordered() const
Definition: Instructions.h:274
SyncScope::ID getSyncScopeID() const
Returns the synchronization scope ID of this load instruction.
Definition: Instructions.h:255
Align getAlign() const
Return the alignment of the access that is being performed.
Definition: Instructions.h:236
static LocationSize precise(uint64_t Value)
Metadata node.
Definition: Metadata.h:1067
This class implements a map that also provides access to all stored values in a deterministic order.
Definition: MapVector.h:36
Representation for a specific memory location.
Function * getFunction(StringRef Name) const
Look up the specified function in the module symbol table.
Definition: Module.cpp:191
const DataLayout & getDataLayout() const
Get the data layout for the module's target platform.
Definition: Module.h:287
void addIncoming(Value *V, BasicBlock *BB)
Add an incoming value to the end of the PHI list.
static PHINode * Create(Type *Ty, unsigned NumReservedValues, const Twine &NameStr, BasicBlock::iterator InsertBefore)
Constructors - NumReservedValues is a hint for the number of incoming edges that this phi node will h...
void setIncomingValue(unsigned i, Value *V)
Value * getIncomingValueForBlock(const BasicBlock *BB) const
BasicBlock * getIncomingBlock(unsigned i) const
Return incoming basic block number i.
Value * getIncomingValue(unsigned i) const
Return incoming value number x.
unsigned getNumIncomingValues() const
Return the number of incoming edges.
static PoisonValue * get(Type *T)
Static factory methods - Return an 'poison' object of the specified type.
Definition: Constants.cpp:1827
A set of analyses that are preserved following a run of a transformation pass.
Definition: Analysis.h:109
static PreservedAnalyses all()
Construct a special preserved set that preserves all passes.
Definition: Analysis.h:115
void preserve()
Mark an analysis as preserved.
Definition: Analysis.h:129
Helper class for SSA formation on a set of values defined in multiple blocks.
Definition: SSAUpdater.h:40
void RewriteUse(Use &U)
Rewrite a use of the symbolic value.
Definition: SSAUpdater.cpp:188
void Initialize(Type *Ty, StringRef Name)
Reset this object to get ready for a new set of SSA updates with type 'Ty'.
Definition: SSAUpdater.cpp:53
void UpdateDebugValues(Instruction *I)
Rewrite debug value intrinsics to conform to a new SSA form.
Definition: SSAUpdater.cpp:200
void AddAvailableValue(BasicBlock *BB, Value *V)
Indicate that a rewritten value is available in the specified block with the specified value.
Definition: SSAUpdater.cpp:70
This class represents the LLVM 'select' instruction.
size_type size() const
Definition: SmallPtrSet.h:94
size_type count(ConstPtrType Ptr) const
count - Return 1 if the specified pointer is in the set, 0 otherwise.
Definition: SmallPtrSet.h:360
std::pair< iterator, bool > insert(PtrType Ptr)
Inserts Ptr if and only if there is no element in the container equal to Ptr.
Definition: SmallPtrSet.h:342
SmallPtrSet - This class implements a set which is optimized for holding SmallSize or less elements.
Definition: SmallPtrSet.h:427
SmallSet - This maintains a set of unique values, optimizing for the case when the set is small (less...
Definition: SmallSet.h:135
std::pair< const_iterator, bool > insert(const T &V)
insert - Insert an element into the set if it isn't already there.
Definition: SmallSet.h:179
bool empty() const
Definition: SmallVector.h:94
size_t size() const
Definition: SmallVector.h:91
This class consists of common code factored out of the SmallVector class to reduce code duplication b...
Definition: SmallVector.h:586
void assign(size_type NumElts, ValueParamT Elt)
Definition: SmallVector.h:717
reference emplace_back(ArgTypes &&... Args)
Definition: SmallVector.h:950
void resize(size_type N)
Definition: SmallVector.h:651
void push_back(const T &Elt)
Definition: SmallVector.h:426
This is a 'vector' (really, a variable-sized array), optimized for the case when the array is small.
Definition: SmallVector.h:1209
Multiway switch.
Analysis pass providing the TargetTransformInfo.
Analysis pass providing the TargetLibraryInfo.
Provides information about what library functions are available for the current target.
This pass provides access to the codegen interfaces that are needed for IR-level transformations.
bool hasBranchDivergence(const Function *F=nullptr) const
Return true if branch divergence exists.
@ TCK_SizeAndLatency
The weighted sum of size and latency.
@ TCC_Free
Expected to fold away in lowering.
InstructionCost getInstructionCost(const User *U, ArrayRef< const Value * > Operands, TargetCostKind CostKind) const
Estimate the cost of a given IR user when lowered.
The instances of the Type class are immutable: once they are created, they are never changed.
Definition: Type.h:45
bool isVectorTy() const
True if this is an instance of VectorType.
Definition: Type.h:265
static IntegerType * getInt1Ty(LLVMContext &C)
bool isIntegerTy() const
True if this is an instance of IntegerType.
Definition: Type.h:228
'undef' values are things that do not have specified contents.
Definition: Constants.h:1350
static UndefValue * get(Type *T)
Static factory methods - Return an 'undef' object of the specified type.
Definition: Constants.cpp:1808
A Use represents the edge between a Value definition and its users.
Definition: Use.h:43
void setOperand(unsigned i, Value *Val)
Definition: User.h:174
Value * getOperand(unsigned i) const
Definition: User.h:169
See the file comment.
Definition: ValueMap.h:84
iterator find(const KeyT &Val)
Definition: ValueMap.h:155
iterator end()
Definition: ValueMap.h:135
LLVM Value Representation.
Definition: Value.h:74
Type * getType() const
All values are typed, get the type of this value.
Definition: Value.h:255
const Value * DoPHITranslation(const BasicBlock *CurBB, const BasicBlock *PredBB) const
Translate PHI node to its predecessor from the given basic block.
Definition: Value.cpp:1066
bool hasOneUse() const
Return true if there is exactly one use of this value.
Definition: Value.h:434
void replaceAllUsesWith(Value *V)
Change all uses of this to point to a new Value.
Definition: Value.cpp:534
const Value * stripPointerCasts() const
Strip off pointer casts, all-zero GEPs and address space casts.
Definition: Value.cpp:693
bool use_empty() const
Definition: Value.h:344
LLVMContext & getContext() const
All values hold a context through their type.
Definition: Value.cpp:1074
StringRef getName() const
Return a constant reference to the value's name.
Definition: Value.cpp:309
void takeName(Value *V)
Transfer the name from V to this value.
Definition: Value.cpp:383
std::pair< iterator, bool > insert(const ValueT &V)
Definition: DenseSet.h:206
self_iterator getIterator()
Definition: ilist_node.h:109
NodeTy * getNextNode()
Get the next node, or nullptr for the list tail.
Definition: ilist_node.h:316
@ C
The default llvm calling convention, compatible with C.
Definition: CallingConv.h:34
StringRef getName(ID id)
Return the LLVM name for an intrinsic, such as "llvm.ppc.altivec.lvx".
Definition: Function.cpp:1017
BinaryOp_match< LHS, RHS, Instruction::Add > m_Add(const LHS &L, const RHS &R)
class_match< Constant > m_Constant()
Match an arbitrary Constant and ignore it.
Definition: PatternMatch.h:160
bool match(Val *V, const Pattern &P)
Definition: PatternMatch.h:49
class_match< ConstantInt > m_ConstantInt()
Match an arbitrary ConstantInt and ignore it.
Definition: PatternMatch.h:163
auto m_LogicalOr()
Matches L || R where L and R are arbitrary values.
class_match< CmpInst > m_Cmp()
Matches any compare instruction and ignore it.
Definition: PatternMatch.h:105
class_match< Value > m_Value()
Match an arbitrary value and ignore it.
Definition: PatternMatch.h:92
auto m_LogicalAnd()
Matches L && R where L and R are arbitrary values.
match_combine_or< LTy, RTy > m_CombineOr(const LTy &L, const RTy &R)
Combine two pattern matchers matching L || R.
Definition: PatternMatch.h:234
initializer< Ty > init(const Ty &Val)
Definition: CommandLine.h:450
This is an optimization pass for GlobalISel generic memory operations.
Definition: AddressRanges.h:18
bool RemoveRedundantDbgInstrs(BasicBlock *BB)
Try to remove redundant dbg.value instructions from given basic block.
bool all_of(R &&range, UnaryPredicate P)
Provide wrappers to std::all_of which take ranges instead of having to pass begin/end explicitly.
Definition: STLExtras.h:1731
bool ConstantFoldTerminator(BasicBlock *BB, bool DeleteDeadConditions=false, const TargetLibraryInfo *TLI=nullptr, DomTreeUpdater *DTU=nullptr)
If a terminator instruction is predicated on a constant value, convert it into an unconditional branc...
Definition: Local.cpp:129
unsigned replaceNonLocalUsesWith(Instruction *From, Value *To)
Definition: Local.cpp:3434
auto successors(const MachineBasicBlock *BB)
MDNode * getBranchWeightMDNode(const Instruction &I)
Get the branch weights metadata node.
Value * findAvailablePtrLoadStore(const MemoryLocation &Loc, Type *AccessTy, bool AtLeastAtomic, BasicBlock *ScanBB, BasicBlock::iterator &ScanFrom, unsigned MaxInstsToScan, BatchAAResults *AA, bool *IsLoadCSE, unsigned *NumScanedInst)
Scan backwards to see if we have the value of the given pointer available locally within a small numb...
Definition: Loads.cpp:582
bool SimplifyInstructionsInBlock(BasicBlock *BB, const TargetLibraryInfo *TLI=nullptr)
Scan the specified basic block and try to simplify any instructions in it and recursively delete dead...
Definition: Local.cpp:724
void DeleteDeadBlock(BasicBlock *BB, DomTreeUpdater *DTU=nullptr, bool KeepOneInputPHIs=false)
Delete the specified block, which must have no predecessors.
Value * FindAvailableLoadedValue(LoadInst *Load, BasicBlock *ScanBB, BasicBlock::iterator &ScanFrom, unsigned MaxInstsToScan=DefMaxInstsToScan, BatchAAResults *AA=nullptr, bool *IsLoadCSE=nullptr, unsigned *NumScanedInst=nullptr)
Scan backwards to see if we have the value of the given load available locally within a small number ...
Definition: Loads.cpp:453
BasicBlock * DuplicateInstructionsInSplitBetween(BasicBlock *BB, BasicBlock *PredBB, Instruction *StopAt, ValueToValueMapTy &ValueMapping, DomTreeUpdater &DTU)
Split edge between BB and PredBB and duplicate all non-Phi instructions from BB between its beginning...
void setBranchWeights(Instruction &I, ArrayRef< uint32_t > Weights)
Create a new branch_weights metadata node and add or overwrite a prof metadata reference to instructi...
Value * simplifyInstruction(Instruction *I, const SimplifyQuery &Q)
See if we can compute a simplified version of this instruction.
Interval::pred_iterator pred_end(Interval *I)
Definition: Interval.h:112
bool any_of(R &&range, UnaryPredicate P)
Provide wrappers to std::any_of which take ranges instead of having to pass begin/end explicitly.
Definition: STLExtras.h:1738
bool isInstructionTriviallyDead(Instruction *I, const TargetLibraryInfo *TLI=nullptr)
Return true if the result produced by the instruction is not used, and the instruction will return.
Definition: Local.cpp:399
bool isGuard(const User *U)
Returns true iff U has semantics of a guard expressed in a form of call of llvm.experimental....
Definition: GuardUtils.cpp:18
bool TryToSimplifyUncondBranchFromEmptyBlock(BasicBlock *BB, DomTreeUpdater *DTU=nullptr)
BB is known to contain an unconditional branch, and contains no instructions other than PHI nodes,...
Definition: Local.cpp:1113
auto reverse(ContainerTy &&C)
Definition: STLExtras.h:428
bool hasValidBranchWeightMD(const Instruction &I)
Checks if an instructions has valid Branch Weight Metadata.
raw_ostream & dbgs()
dbgs() - This returns a reference to a raw_ostream for debugging messages.
Definition: Debug.cpp:163
Interval::pred_iterator pred_begin(Interval *I)
pred_begin/pred_end - define methods so that Intervals may be used just like BasicBlocks can with the...
Definition: Interval.h:109
Constant * ConstantFoldCastOperand(unsigned Opcode, Constant *C, Type *DestTy, const DataLayout &DL)
Attempt to constant fold a cast with the specified operand.
void cloneNoAliasScopes(ArrayRef< MDNode * > NoAliasDeclScopes, DenseMap< MDNode *, MDNode * > &ClonedScopes, StringRef Ext, LLVMContext &Context)
Duplicate the specified list of noalias decl scopes.
cl::opt< unsigned > DefMaxInstsToScan
The default number of maximum instructions to scan in the block, used by FindAvailableLoadedValue().
void SplitLandingPadPredecessors(BasicBlock *OrigBB, ArrayRef< BasicBlock * > Preds, const char *Suffix, const char *Suffix2, SmallVectorImpl< BasicBlock * > &NewBBs, DomTreeUpdater *DTU=nullptr, LoopInfo *LI=nullptr, MemorySSAUpdater *MSSAU=nullptr, bool PreserveLCSSA=false)
This method transforms the landing pad, OrigBB, by introducing two new basic blocks into the function...
Constant * ConstantFoldBinaryOpOperands(unsigned Opcode, Constant *LHS, Constant *RHS, const DataLayout &DL)
Attempt to constant fold a binary operation with the specified operands.
void combineMetadataForCSE(Instruction *K, const Instruction *J, bool DoesKMove)
Combine the metadata of two instructions so that K can replace J.
Definition: Local.cpp:3310
BasicBlock * SplitBlockPredecessors(BasicBlock *BB, ArrayRef< BasicBlock * > Preds, const char *Suffix, DominatorTree *DT, LoopInfo *LI=nullptr, MemorySSAUpdater *MSSAU=nullptr, bool PreserveLCSSA=false)
This method introduces at least one new basic block into the function and moves some of the predecess...
void MergeBasicBlockIntoOnlyPred(BasicBlock *BB, DomTreeUpdater *DTU=nullptr)
BB is a block with one predecessor and its predecessor is known to have one successor (BB!...
Definition: Local.cpp:764
auto lower_bound(R &&Range, T &&Value)
Provide wrappers to std::lower_bound which take ranges instead of having to pass begin/end explicitly...
Definition: STLExtras.h:1963
Value * simplifyCmpInst(unsigned Predicate, Value *LHS, Value *RHS, const SimplifyQuery &Q)
Given operands for a CmpInst, fold the result or return null.
void findDbgValues(SmallVectorImpl< DbgValueInst * > &DbgValues, Value *V, SmallVectorImpl< DPValue * > *DPValues=nullptr)
Finds the llvm.dbg.value intrinsics describing a value.
Definition: DebugInfo.cpp:137
void adaptNoAliasScopes(llvm::Instruction *I, const DenseMap< MDNode *, MDNode * > &ClonedScopes, LLVMContext &Context)
Adapt the metadata for the specified instruction according to the provided mapping.
auto max_element(R &&Range)
Definition: STLExtras.h:1995
Constant * ConstantFoldInstruction(Instruction *I, const DataLayout &DL, const TargetLibraryInfo *TLI=nullptr)
ConstantFoldInstruction - Try to constant fold the specified instruction.
bool isGuaranteedNotToBeUndefOrPoison(const Value *V, AssumptionCache *AC=nullptr, const Instruction *CtxI=nullptr, const DominatorTree *DT=nullptr, unsigned Depth=0)
Return true if this function can prove that V does not have undef bits and is never poison.
bool isSafeToSpeculativelyExecute(const Instruction *I, const Instruction *CtxI=nullptr, AssumptionCache *AC=nullptr, const DominatorTree *DT=nullptr, const TargetLibraryInfo *TLI=nullptr)
Return true if the instruction does not have any effects besides calculating the result and does not ...
bool isGuaranteedToTransferExecutionToSuccessor(const Instruction *I)
Return true if this function can prove that the instruction I will always transfer execution to one o...
bool extractBranchWeights(const MDNode *ProfileData, SmallVectorImpl< uint32_t > &Weights)
Extract branch weights from MD_prof metadata.
void erase_if(Container &C, UnaryPredicate P)
Provide a container algorithm similar to C++ Library Fundamentals v2's erase_if which is equivalent t...
Definition: STLExtras.h:2060
auto predecessors(const MachineBasicBlock *BB)
bool is_contained(R &&Range, const E &Element)
Returns true if Element is found in Range.
Definition: STLExtras.h:1888
bool pred_empty(const BasicBlock *BB)
Definition: CFG.h:118
Instruction * SplitBlockAndInsertIfThen(Value *Cond, BasicBlock::iterator SplitBefore, bool Unreachable, MDNode *BranchWeights=nullptr, DomTreeUpdater *DTU=nullptr, LoopInfo *LI=nullptr, BasicBlock *ThenBlock=nullptr)
Split the containing block at the specified instruction - everything before SplitBefore stays in the ...
void array_pod_sort(IteratorTy Start, IteratorTy End)
array_pod_sort - This sorts an array with the specified start and end extent.
Definition: STLExtras.h:1616
void identifyNoAliasScopesToClone(ArrayRef< BasicBlock * > BBs, SmallVectorImpl< MDNode * > &NoAliasDeclScopes)
Find the 'llvm.experimental.noalias.scope.decl' intrinsics in the specified basic blocks and extract ...
BasicBlock * SplitEdge(BasicBlock *From, BasicBlock *To, DominatorTree *DT=nullptr, LoopInfo *LI=nullptr, MemorySSAUpdater *MSSAU=nullptr, const Twine &BBName="")
Split the edge connecting the specified blocks, and return the newly created basic block between From...
unsigned pred_size(const MachineBasicBlock *BB)
static auto filterDbgVars(iterator_range< simple_ilist< DbgRecord >::iterator > R)
Filter the DbgRecord range to DPValue types only and downcast.
void FindFunctionBackedges(const Function &F, SmallVectorImpl< std::pair< const BasicBlock *, const BasicBlock * > > &Result)
Analyze the specified function to find all of the loop backedges in the function and return them.
Definition: CFG.cpp:34
std::optional< bool > isImpliedCondition(const Value *LHS, const Value *RHS, const DataLayout &DL, bool LHSIsTrue=true, unsigned Depth=0)
Return true if RHS is known to be implied true by LHS.
A collection of metadata nodes that might be associated with a memory access used by the alias-analys...
Definition: Metadata.h:760
Function object to check whether the second component of a container supported by std::get (like std:...
Definition: STLExtras.h:1468